WV Sharan - on demand camper under $130

Use the boot!

If it's not flat (as with my 5 seater) - use it for storage. Get some durable boxes that will hold your weight. If it's flat - skip to page 3 :)

1

Bed rack

Light, durable and flat surface to  put your mattress on - plywood works great and is cheap. Make sure it's easy to put in and out

2

Car bed / mattress

Make it comfy but also durable.  An air mattress might not last long, I suggest rebonded foam sheets.

3