In this design I lay the mattress on the floor, and cut out the mattress to fit inbetween the wheel wells, like this...
It lays down nice and flat, and you don't even know that you are sleeping on the wheel wells.
With that in mind, you could build a very comfortable teardrop at 10' long and 78" high on your HF chassis.

there's no storage in the front, but you do have a galley!
Mike...