A little different take on the concept...
This one has walls just over 4' high (including lift-top; main body wall are less), the body is still at 9' long. The top lifts as in the WW, the front lifts the same way, then the wall/floor for the bed area flips down. You now have 4' between the bed and the back wall, and 6'4" standing room. The bed (above mattress) has about 32" clearance at the apex of the curve, 41" at the hinge. The front lift-up is shaped to drain when open, which is the major limiting factor on the tear-drop profile.
Nothing can go on the tongue, and of course no rear galley, but the closed height should be below most trucks, and the open height is quite comfortable. Again, the bed is lengthwise; more room could be gained by turning it sideways.
edit --- I see after posting that the top profile is a bit different than the other two, but you get the idea...