Hi,
I don't completely understand your design, or goals, but the complicated fold out design could sure be a pain!
As someone suggested, a standy (trailer you can stand up in) would be much easier...
Another option, if the extra height is just for the shower and toilet, is to do just a large teardrop with sitdown shower.
A dropped floor, and little bigger than usual teardrop shape can accomodate your needs.
Rob