For under $400 you can get a rubbermaid utility shed that's about 4x6' on the inside and close to 5x7 on the outside. It would be tempting to try cutting some windows
into one of those and making a teardrop style camper for under $1000. Of course the "headroom" is around four feet, but it slides back for easy access. I'm tempted to try it. It would be a fun project, and I bet I could get my investment back.
Storage Capacity: 92 cubic feet
Inside Dimensions: 49 inches wide x 70 inches deep x 46 inches high
(Exterior is something like 60x80x54)
Structural foam floor supports up to 1,300 lbs/590.2 kg
Lid slides back for easy walk-in access