I have a camper interior for a 2-door Beetle. It's a six foot L-shaped plywood deck that replaces the back and shotgun seats. And a 12V thermoelectric cooler. I've got a 12V coffee pot now but I haven't had a chance to use it.
It's currently in storage in the shell of the '58 Baja. When it was installed in the Superbeetle I overnighted at Bonneville Salt Flats and the Summit of Donner Pass.
The Superbeetle spare tire is positioned where you could have a composting toilet there instead. Maybe a modesty curtain to hang on the hood.
Bucky Fuller said a house should cost as much as a car. At least the debt servicing is falling into line.