8×12
Box Footprint
Steel-Framed · Stationary Build
A Solid Steel-Framed Cabin On A Trailer Frame
Forget the lightweight road-camper plan — this is built to sit. Each unit is a solid 8×12 box on a used trailer frame, with the floor raised up over the wheels so the interior is flat and a full 8 ft wide — and the space underneath boxed in as enclosed storage. Metal studs, a real metal roof, one plan cut once and built three times.
20 ga
Steel Studs (min)
Raised
Floor Over Wheels
×3
Frames On Hand
Read This First · For DJ
Build It Solid, Not Light
The old plan treated this like a highway camper — thin wood, weight paranoia, road gear. Scrap that. These sit in one spot and get towed slowly across the yard maybe once or twice a year, so we can build heavier and straighter. Steel studs, a real metal roof, and a proper insulated shell. Don't spend a dollar on the wheels.
What Changes When It Just Sits
- Ignore the wheels. DJ — don't rebuild hubs, pack bearings, or buy new tires. The tires only need to survive an occasional slow tow across the property. Chock and block it.
- No highway weight limit. So frame it in steel and roof it in metal. Solid beats light here.
- Flat 8-ft-wide floor. We deck the floor up and over the wheels, so the whole 8×12 interior is flat and unobstructed — no wheel humps eating your floor space.
- Skip road lighting & brakes. None of it matters for a unit that stays parked.
What You Still Have To Get Right
- Level the frame first. On blocks and drop-leg jack stands, dead level and non-rocking. A racked frame telegraphs into every wall and door.
- Break the thermal bridge. Steel studs conduct cold straight through a wall — continuous exterior foam is not optional (details below).
- Keep water off the steel. Rust is the enemy now, not weight. Isolate steel-to-wood contact and coat the frame.
- Tie it down. A light box on a frame is a sail in a storm — ground anchors and straps.
The plan — three dried-in shells first. Don't try to finish one out top-to-bottom before touching the next. Get all three to a weathertight, lockable shell — frame, raised floor + storage bay, steel-stud walls, roof, door and windows in, wrapped and sided — then stop. Three dry shells you can lock up and finish out one at a time, on your own schedule. That's how we start now instead of waiting to have everything for a complete build.
The Three Frames
Prep Each Frame The Same Way
All three get the identical prep so the builds are interchangeable. Do the best frame first as the prototype, then repeat. The frame is your foundation now — treat it like one.
01
Inspect & Rank
Check all three: main rails, cross members, coupler, welds. Pick the straightest, soundest one to build first. Note any cracked welds to re-weld before decking.
02
Strip Road Gear
Leave one rollable set of tires for towing; otherwise ignore the running gear entirely. No new hubs, bearings, tires, lights, or brakes. Don't spend there.
03
De-Rust & Coat
Wire-wheel the frame, hit bare spots with rust converter, then two coats of rust-inhibiting enamel over the whole thing. This is the part water attacks for the next 20 years.
04
Level & Stabilize
Set on solid blocking with drop-leg jack stands at all four corners plus mid-span on long frames. Get it dead level and rock-free before anything goes on top.
05
Sill & Barrier
Bolt a pressure-treated 2x sill (or steel hat channel) to the frame with sill-seal or ice-and-water membrane between steel and wood, so the two never sit wet against each other.
06
Raise The Floor
Set steel-tube or treated risers on the frame rails tall enough to clear the tires, then joists at 16″ OC and 3/4″ T&G plywood on top. The floor decks up and over the wheels for a flat 8-ft interior — and frame the enclosed storage bay underneath before you close it in (next section).
The Spec DJ Asked For
Metal Stud Framing
This is the part that makes it solid. Light-gauge steel framing is cheap, dead-straight, bug-proof, and fire-resistant — and because these never see highway flex, it's the right call. Spec heavier gauge than a drywall partition; this is structure.
Members & Fasteners
- Walls: 3⅝″ steel studs, 20-gauge (33 mil) minimum, at 16″ on center, in matching 20-ga steel track top and bottom. Interior-only partitions can drop to 25-ga.
- Roof: 6″ or 8″ steel joists (or heavier studs) as rafters at 16″ OC on a mono-slope (shed) pitch — even parked, water has to run off.
- Screws: #8 self-drilling (self-tapping) framing screws for stud-to-track; #10 at member-to-member high-load points.
- Openings: double the studs (box header) around the door, window, and AC opening; add solid blocking for hinges, latches, and the AC's weight.
The Steel Details People Miss
- Thermal bridge: sheathe the outside in 1–2″ of continuous rigid foam (XPS or polyiso) over the studs before siding. Steel wicks cold through a wall — skip this and you get cold spots and condensation.
- Corrosion: use galvanized (G60 or better) studs and track; keep steel out of standing water; touch up cut ends.
- Cavity insulation: mineral-wool or foam batt in the stud bays — but the continuous exterior foam is what makes a steel wall actually perform.
- Wiring: use plastic grommets/bushings in the pre-punched stud holes so wire never chafes on cut steel.
Why steel here: on a unit that never flexes down a highway, steel studs give you straight, stable, bug- and fire-resistant walls that all three cabins share to the sixteenth of an inch. Cut one accurate stud list, then repeat it three times — that repeatability is the whole point of building three.
Assemblies
Floor, Wall & Roof Stack-Ups
Same 8×12 layout in every unit. The floor is raised over the wheels, so it's flat wall-to-wall — and the heavy, wet, and bulky stuff (water, batteries, tools, gray tank) drops into the enclosed bay below instead of eating interior space.
Front / UtilityBreaker panel and shore inlet; water and batteries live in the belly bay below.
Wet Bath32x32 shower pan, FRP walls, curtain, cassette toilet, exhaust fan.
Door + ACSteel door and window AC framed into a boxed, double-stud opening with real support.
Kitchen WallSink, pump, jugs, mini fridge under counter, microwave on a shelf.
Rear BedFull-width bed platform across the back, storage below.
8×12 box — this is the finish-out (phase 2) target. Dry the shell in first; the studs and openings are already framed for exactly this layout.
Assembly Stack-Ups (inside → out)
Floor (raised over wheels): coated steel frame → sill membrane → steel-tube/treated risers tall enough to clear the tires → joists 16″ OC → 3/4″ T&G plywood, glued + screwed → finish floor. The gap the risers create is the belly storage.
Wall: interior panel → 20-ga steel studs 16″ OC with mineral-wool batt → exterior sheathing → housewrap (WRB) → 1–2″ continuous rigid foam → furring → corrugated steel or fiber-cement siding.
Roof: ceiling panel → steel rafters 16″ OC with batt → sheathing → underlayment → standing-seam or corrugated metal on a shed slope, with a real overhang and drip edge.
The rule: water leaves the roof, runs down the siding, and never touches the steel frame. Everything above drains onto the ground, not into the wall.
Under the floor — belly storage: raising the deck over the wheels leaves an enclosed bay between the frame rails. Box the wheels into their own wells, then skin the sides with treated ply or metal skirting and cut exterior access hatches fore and aft of the axle. Build that bay now and leave it ready — the water tanks, batteries, and gray tank go in later during finish-out, low and centered over the axle for balance, out of your living space. Just frame and skin it before the deck goes down; you can't get to it afterward.
Materials
Shopping List (Per Unit)
Buy for one unit, confirm the build, then multiply by three and order in bulk. Steel studs, screws, foam, and roofing all get cheaper by the pallet.
Structure & Shell
- 3⅝″ 20-ga steel studs + matching track (walls at 16″ OC)
- 6″/8″ steel joists for floor joists and roof rafters
- #8 self-drilling framing screws (buy in bulk)
- 3/4″ T&G plywood subfloor + construction adhesive
- 1–2″ rigid foam (XPS/polyiso), housewrap, butyl/flashing tape
- Corrugated metal siding + metal roof panels, closures, screws w/ washers
- Mineral-wool or foam batt for the stud and rafter bays
Openings & Systems
- Steel exterior door + one or two windows (buy used to save)
- Through-wall or window AC — verify it's not a recalled Midea first
- 32x32 shower pan + FRP wall panels, cassette/portable toilet, exhaust fan
- Bar sink, faucet, 12V demand pump, fresh + gray water jugs
- Shore-power inlet, GFCI, small breaker panel, LED lights, wire + bushings
- Used mini fridge, microwave, and a bed platform
Shop The Systems — Amazon
Bulk steel, foam, and siding come from a steel supplier or Home Depot. These are the finish-out parts Amazon ships to your door — one link per item:
- Window AC unit
- Mini fridge
- Countertop microwave
- Cassette / portable toilet
- 32×32 shower pan
- Bar sink + faucet
- 12V water pump
- Water storage jugs
- Shore-power inlet
- GFCI outlets
- 12V LED lights
- Self-drilling framing screws
- Rigid foam board
- Flashing / butyl tape
As an Amazon Associate, CargoSolar earns from qualifying purchases.
Window-AC warning: only mount a unit through the wall if it can breathe exactly as its manual requires — side vents can't be buried in a framed wall. And before you frame a permanent opening, confirm the unit isn't a recalled Midea U/U+. See the Midea recall guide for how to check and what to do.
Cut List
8×12 Shell — Steel Cut List (Per Unit)
The per-shell takeoff for one dried-in 8×12 unit — multiply by three. Assumes 3⅝″ 20-ga studs at 16″ OC, 6″ joists for floor and roof, a 2:12 shed slope (7′0″ low eave to 8′4″ high eave), a 32″×80″ steel door, and two windows. Only the floor risers depend on DJ's frame numbers.
| Member | Cut / Size | Qty (per unit) |
|---|---|---|
| Steel framing — 3⅝″ 20-ga studs & 6″ joists | ||
| Long-wall studs — high eave | 8′4″ | 10 |
| Long-wall studs — low eave | 7′0″ | 10 |
| End-wall studs (raked) | 7′0″–8′4″ | 10 (5 per end) |
| King/jack studs at openings | wall height | 8 |
| Wall track, top + bottom | 10′ sticks (~80 lin ft) | 8 |
| Headers — door + 2 windows | boxed from track | 3 |
| Roof rafters | 9′0″ (8′ span + 1′ overhang) | 10 |
| Floor joists | 8′0″ | 10 |
| Floor risers (over the wheels) | height per frame — pending | ~14 |
| Skin & dry-in | ||
| Subfloor, 3/4″ T&G plywood | 4×8 sheet | 3 |
| Wall + roof sheathing | 4×8 sheet | 13 |
| Continuous rigid foam | 4×8 sheet, 1–2″ | 10 |
| Housewrap | 9′ roll | 1 |
| Metal roof panels | 3′ × 9′ | 5 |
| Metal siding | ~400 sq ft | 1 lot |
| Belly skirting + access hatches | wheel wells + 2 doors | 1 set |
| Steel door + windows | 32″×80″ + two | 3 |
| #8 self-drilling framing screws | bulk | ~1,500 |
| Flashing, tape, drip edge, closures, sealant | dry-in kit | 1 set |
Pending from DJ — three numbers per frame: the usable length and width of the frame, and the height from the top of the frame rails to the top of the tire. Those set the riser height (Step 06) and confirm the 8×12 box sits square. Everything else above is locked for the 8×12 shell — send the numbers and we finalize the riser cuts and any length trims.
Budget
Real Numbers — Per Unit & ×3
Split into two phases. The dried-in shell runs about $4,750 per unit — that's the number to price first, since that's what you build now, times three. Finishing out adds about $3,150 a unit later, for roughly $7,900 complete. Target numbers using some used parts (door, window, fridge, AC), not store quotes.
| Category | Per Unit | Notes |
|---|---|---|
| Phase 1 — Dried-In Shell (build now, ×3) | ||
| Frame prep | $350 | De-rust, coat, jack stands, blocking, weld repairs. |
| Raised floor | $650 | Risers over the wheels, joists 16″ OC, 3/4″ T&G subfloor. |
| Belly storage bay | $300 | Wheel wells, skirting/skin, exterior access hatches. |
| Steel studs + track | $900 | 20-ga walls + roof members at 16″ OC. |
| Fasteners + misc steel | $250 | Self-drilling screws, clips, headers, bracing. |
| Housewrap + exterior foam | $500 | WRB and 1–2″ continuous rigid foam under the siding. |
| Flashing, tape, sealants | $200 | Drip edge, butyl tape, caulk. |
| Metal siding + metal roof | $1,100 | Corrugated/standing-seam panels, closures, trim. |
| Steel door + windows | $500 | Used where possible; openings closed = dried in. |
| Shell subtotal | ~$4,750 | Weathertight & lockable. Build all three to here first. |
| Phase 2 — Finish-Out (later, one at a time) | ||
| Cavity insulation | $250 | Mineral-wool or foam batt in the stud bays. |
| Interior panels + flooring | $600 | Wall and ceiling panels, finish floor. |
| Wet bath + toilet | $650 | Shower pan, FRP, cassette toilet, fan. |
| Kitchen + plumbing | $350 | Sink, faucet, pump, jugs, drain, gray tote. |
| Electrical | $450 | Shore inlet, GFCI, breaker box, outlets, lights, wire. |
| Appliances | $400 | Used mini fridge, microwave, window AC if safe. |
| Paint, trim, buffer | $450 | The catch-all that keeps the budget honest. |
| Finish-out subtotal | ~$3,150 | Per unit, on your own schedule. |
| Complete, per unit | ~$7,900 | Shell + finish-out. |
All three: about $14,250 in materials gets all three shells dried in (phase 1) — buy the steel, foam, and roofing for three in one order and that drops 10–15%, so call it ~$12,500 to start. Finishing out adds ~$3,150 a unit as you go; complete, all three lands near $21,000 all-in.
Sequence
Build Order — Shells First
Steps 01–07 are the dried-in shell. Do them on all three frames before you finish out a single interior. Step 08 is phase two, one unit at a time, whenever you're ready.
01
Prototype Shell First
Build unit #1 to a dried-in shell, work out every measurement, then repeat exactly on frames two and three. Don't chase a finished interior until all three shells stand.
02
Prep & Level The Frame
De-rust, coat, block, and level. Set the sill and barrier. This is the foundation — get it flat and solid before anything stands up.
03
Raise Floor + Storage
Risers over the frame rails to clear the tires, then joists 16″ OC and 3/4″ T&G subfloor. Frame and skin the belly storage bay before the deck goes down — you can't reach it after.
04
Stand The Steel Walls
Build the 8×12 wall panels flat on the deck — stud to track with self-drilling screws — then stand, plumb, screw to the sill, tie the corners. Box every opening.
05
Frame The Shed Roof
Steel rafters on a mono-slope with a real overhang. Get the pitch and drip edge right so water leaves the building, not into the walls.
06
Set Door & Windows
Hang the steel door and windows into their boxed openings so the shell actually closes up and locks. Frame the AC opening now even if the unit goes in later.
07
Dry It In
Sheathing, housewrap, continuous foam, metal roof, then metal siding. Now it's weathertight and lockable — that's a finished shell. Repeat 02–07 on the other two frames.
08
Finish Out (Phase 2)
With all three dry and locked, finish interiors one at a time: batt insulation, panels, wet bath, kitchen, electrical, appliances — then final leveling, anchors, and tie-downs.
Before You Build Three
Specs Worth Checking
A few things to confirm before ordering steel for three units — gauge/screw specs, local siting rules, and the AC recall check.
- Steel Framing Industry Association — stud gauge/thickness, track, and screw references for light-gauge steel framing.
- Local building code & siting: check setbacks, tie-down, and whether three stationary units on one lot need a permit before you commit the steel.
- CargoSolar Midea recall guide — verify any window AC before framing it into a permanent wall opening (see also the AP recall report).
The DIY Set
Three Ways To Build Off-Grid Shelter
Pick the path that fits your budget and skills — a solid steel-framed cabin on a trailer frame, a serious 40-foot container home, or the AC recall check you need before you frame any window unit into a wall.
DIY Trailer · ~$8K
Solid 8×12 metal-stud cabin on a used trailer frame — raised floor over the wheels, storage below, built as dried-in shells to finish out.
DIY Conex · $31K
A 40-foot high-cube container turned into a real small home: bedroom, wet bath, kitchen, and a living zone.
Midea Recall
Before you frame a window AC into a wall, check the Midea U/U+ recall — refund rules, cord-cut proof, and the hotline.