My Dad once built a trailer that fitted inside a tent, as a bed-base! Removable tow-bar. The tent was a ridge type which he modified to allow the passage. They slept on a standard mattress in there!

Before I left England, they were advertising car-top tents that clamped onto a roof-rack. You would have to find a car that could support a roof-rack, of course.

I like the look of the campers that fit in the bed of a Ute/Pickup. One that fitted into a trailer (what are trailers called in America?) would give service in two capacities.

Hmmm.