I started with a locally built 16' cargo trailer with 3/4" t&g floor and nothing inside. I had the builder frame for the a/c, powered vent and windows. I took the tanks (45 gal. fresh water, 39 gal. gray, 14 gal. black) to him and explained where I wanted them. He fabricated brackets for each tank. The fresh water tank is between the axles, the gray water is just forward of that with the black tank near the front under the toilet. I also had him install the side door (with a screen door) 25" from the front to allow for the "kitchen".
I undercoated the plywood flooring with diy bed liner, painted the fenders black and added the lights as it only came with 4 on each side.
The trailer is framed with 1" square tube that I added 1/2" furring strips to so I could fit 1-1/2" poly iso insulation throughout, including the ramp. The furring strips also allow for easy attachment of the walls/ceiling panels. I also custom fit backing pieces from 2x4s for the bed frame hinges, mattress supports and tables.
The walls/ceiling are plastic sheets from Home Depot that are intended for commercial bathrooms. Sheets were bent over a 2x4 and heated with a heat gun to accommodate the front slope. I used these sheets for the shower stall too. They are very durable and are easy to clean. The trim strips are vinyl fence trim.
The water supply plumbing is PEX, the waste lines/vents are ABS and the propane plumbing is soldered copper.
View attachment 140495
Two 20 lb. propane tanks with automatic switchover valve/regulator on the tongue. The front shows a gfi ac outlet, spray port and the upper refrigerator vent. The propane furnace vents and lower refrigerator vents are not visible. On the side, leveling jacks, 30 amp ac service, spray port, water inlet (city water/water tank fill), cable, dump plumbing/valves along with Tornado tank flush inlets and a quick disconnect for a propane generator. The window on this side is also an emergency exit. On the other side is the side door with screen door, low profile mounting step and two propane quick disconnects for grill and fire pit.
View attachment 140485 View from the ramp.
View attachment 140486 View from the back, inside. Showing the A/C (heating & air), smoke detector, TV, thermostat, fold out table, gfi outlet and outlets w/usb chargers, distribution panel and in-floor battery box on the "utility wall". 6000 lb. tied downs are bolted into the floor with backing plates on the underside. "Kitchen". Screen door and fold out table on the right wall. The fold out tables are a 2' x 4' Lifetime table purchased from Home Depot which I drilled out the hinge that joined the halves, fabricated wall hinges and hung them.
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Mattress suspended from the ceiling and fold down "bed frame". The flooring is Luxury Vinyl Plank. It is inexpensive, durable, waterproof and easy to install. I fabricated the trim strip on the back side of the flooring.
View attachment 140491 View from near the front. The 4" foam mattress is suspended from the ceiling. The cross straps act as a shelf allowing the mattress to be slid in/out while the center strap holds it securely in place. The center strap is the only one that gets removed. The ramp is painted (with a grit) light gray with darker gray sponged on to yield a relatively light overall color to keep the small space from feeling smaller and provide a camouflage to hide tire tracks. The "bed frames" are hinged with household hinges and held in place with a 1/4-20 knob that goes into a small piece I fabricated and attached to the trailer frame.
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View from the side door. The "utility wall" on the left showing the powered fan vent control, tank monitor, Sirius satellite radio, switches for outdoor understep lights, kitchen light, bathroom lights, propane/CO monitor on the bottom. The bathroom has a small sink not visible on the left, toilet, and the 2x3 shower is on the right.
View attachment 140493
The "kitchen" showing the microwave (held in place with a couple fabricated brackets), cook top, sink, 3 cu. ft. refrigerator/freezer, propane furnace. The top left shows the tv antenna controls.
I hope this helps show what the inside is like and gives you some ideas for your build.
Ray