I've been thinking along the lines of a slide-in as well, but with the possibility later on of putting it onto a trailer chassis as a more "standard" tear.
With that in mind, this episode of DIY's "Wasted Spaces"
http://www.diynetwork.com/diy/shows_dwsp/episode/0,3110,DIY_28376_51554,00.html
has a truck storage box that goes up to the height of the wheel wells, and a standard teardrop body (5 ft wide x whatever length?) could sit on top of it. The middle drawer of the storage box would be widened to the width of the entry, and used for storage of the entry stairs, and the drawers would be shortened to allow a footwell through the floor of the tear itself.
The length would run to the end of the tailgate, rather than being able to close it in with the tailgate, and could probably hang over a little if necessary.
It would end up with a more Benroy-looking profile, and would solve the problem of making either a narrower body to fit between the wheel wells, or requiring a complex structure to wing out over the wheel wells.
It would also regain a lot of the storage area lost (if not actually more) when putting the entry through the galley area.
Any thoughts, good, bad, or otherwise, on that idea?
David