If I were to build my own truck camper, and $$ was not a limitation, I would weld the entire thing myself out of 304 stainless steel tube and sheet. The exterior would be powder coated white.
The entire carcass and some of the inside would be stainless: the frame; siding; roof; bottom; inside divider wall frames; cabinet frames, drawers, shelves, faces, doors, countertops, drawer and door handles; the bath/shower enclosure and fixtures; kitchen walls, sink and fixtures; range top and hood; microwave; refrigerator; window and vent frames; appliance vents, exterior access panels and storage compartment doors and latches; the floor would be stainless tread plate; the tanks would be stainless sheet, welded into the camper framing.
All the siding and roof seams would be welded in continuous, watertight beads. There would be very little opportunity for water intrusion. If water were to get in, there is very little consumable material for it to damage.
The camper would be a flatbed design, with full width bottom and floor and lots of built in exterior storage along the bottom sides and upper side interior storage cabinets. It would be a relatively small camper, 9 feet floor length, 80" width and 6'6" interior height.
The overcab bed would be an east/west orientation, 54x75 double size, with a storage cabinet across the front wall. It would not be a basement design, in order to keep the overall height low. There would be no slides, to simplify construction, reduce weight and reduce chance of leaking.
The camper layout would have a front wet bath/shower, front fridge and wardrobe, rear kitchen, rear dinette area and large rear entry door about 36" wide. The dinette area bed would be a convertible couch-bed, 48x75.
The roof would have no appliance or tank vents or skylights, completely smooth and hole-free. All the vents would be on the side and rear walls. There would be no front overcab window. There would be rack bars welded on the roof for carrying a canoe.
It would have tinted polycarbonate windows, double glazed. The side overcab windows and the dinette window would be the pop-out emergency exit type, since there is no emergency exit vent in the roof. The bathroom would have an operable window and an electric vent fan, through the rear wall. It would have a medium size kitchen window, large side wall dinette area window and small rear wall dinette area window.
Interior would have an accoustic cieling and walls in all but the kitchen and bath, which would be stainless sheet. The floor and step to overcab bed would be Rhino lined, over stainless tread sheet. Insulation would be 1-1/2" hard foam board in the walls, roof and bottom.
Jacks would be mechanical crank-ups, built from modified gooseneck trailer landing gear jacks, with a 2x2 tube welded horizontally at the top to mount them that slides into a receiver tube built into the frame of the camper at each corner of the camper. The jacks would be removable with a hitch pin, accessed through the outside storage compartments. The jacks can store laying down in one of the lower side storage compartments, or be left at home, or stored on the trailer, if towing. The jacks could also be removed, rotated 90* and slid back into the receiver tubes and store horizontally, along the outside of the bottom sides of the camper.
Exterior of the camper would have radius corners at the side walls and roof, like a horse trailer. The overcab front cap would be flat with radius corners, like a gooseneck horse trailer. The windows would have radius corners. The rear entry door would have upper radius corners. There would be a rear awning.
The flatbed the camper loads on would have an 80x108 deck, made for mounting on a 60" cab to axle length single rear wheel 1-ton cab/chassis truck. It would have a 42" high, 60" top width headache rack, just above cab height. The bed would be built of galvanized steel c-channel and tread plate, powder coated black. There would be a galvanized steel 18x18x42 storage cabinet under each side of the bed, ahead of the rear wheels and an 18x18x30 storage cabinet under each side of the bed behind the rear wheels, powder coated black. The bed would have a 2-1/2" receiver hitch built into the frame of the rear apron/step bumper.
The flatbed would have a 30x80 tailgate that folds down into a rear porch, with a hinged telescoping step ladder attached to the pass side end of the tailgate for side entry to the porch. When the tailgate is up, the ladder folds across the back of the tailgate, held in place by hitch pins and pin tabs on the tailgate. The tailgate would have tie down points for tying down extra cargo, bikes, gas jugs, cooler, etc when traveling with the tailgate down. The flat bed would have mounting tabs in each corner to attach the camper to the bed with hitch pins.
-3-burner gas drop-in range
-range hood with vent fan venting through side wall
-3-way 4 cu ft fridge with side wall vents
-gas/electric self starting 6 gal water heater
-gas forced air ducted thermostatic furnace
-12vdc water pump
-9K btu AC built into upper inside cabinet, venting through side or rear wall
-110vac/12vdc coverter/smart charger/solar controller and 12vdc/110vac inverter in exterior side compartment
-3 or 4 AGM 12vdc batteries in exterior side compartment
-roof top solar panels
-Honda 3000euis generator on slide out tray in exterior side compartment
-LED lighting interior and exterior
-stereo/cd/mp3, 3 amps, 6 inside speakers plus sub, 4 outside speakers
-cb/10m radio, 400 watt amp, 102" whip
-110vac and 12vdc outlets in overcab area, kitchen area and outside
-6 pin commercial trailer plug connection to truck
-2 pin heavy duty power connection to truck
-continuous duty solenoid switch for truck battery connection
-30 gal fresh tank
-20 gal grey tank
-cassette toilet, accessed through exterior side panel
-bathroom shower, no sink
-single 30 gal horizontal forklift propane tank in exterior side compartment
The 159" wheelbase supercab single rear wheel one-ton 4wd chassis truck would run 285/75-18E all terrain tires with 4080 lb weight rating on custom 18x8 heavy duty steel wheels with matching weight rating, for max 8160 lb rear axle/tire/wheel load capacity. Heavy duty rear 7-leaf spring packs and 3-leaf overload packs would be sized according to the loaded rear axle weight. The truck would use custom valved Bilstein 5100 shocks.
The truck's drivetrain would consist of a Cummins ISB 5.9 12 valve turbo diesel with exhaust brake, NV5600 6-speed manual granny gear transmission, US Gear 1.2 ratio 2-speed underdrive aux transmission, NP205 4wd transfer case, Dana 60 high pinion front axle with king pins and manual locking hubs, front axle suspension on 3-leaf springs with a tracking bar, Dana 80 rear axle with disc brakes, driveline mounted parking brake drum, hydroboost brake booster, 4.10 axle ratio and Lock Right locking rear differential.
The truck frame would use 60kpsi formed c-channel 10x3x1/4, straight rails front to rear, 34" rail spacing, 7 fabricated cross members huck bolted to the rails. The body/cab would be from a '92-'97 Ford, SuperCab 2-door, with XLT interior. The chassis would carry a 30 gal midship fuel tank inside the driver side frame rail and a 20 gal rear fuel tank behind the axle. Spare tire mounts under the rear tank.