Thanks for these great suggestions, everyone.
If the axle is moved back a total of 11", the outer shell happens to be perfectly balanced on the axle, 80 sq ft front and back of it, leaving the rear bed (say it is a 80 pound structure) against the bulk of the trailer frame; I'm estimating the tongue weight of 75 pounds with these considerations. If I need more tongue weight from there, I would be glad to tongue mount a large lead-acid battery, but if I can keep on the light end of angib's weight graph I would be around 750 lbs total, so 75 lb tongue would be about right.
I redrew the door as big as seems practical with these lines and it came out at 35" at the peak above the bed frame and 25" wide; seems doable with some head tilting in and out. Keeping the door outline near the facet makes sense since that will be one of the stiffest areas, but yes I was forgetting to account for the needs of a recessed door.
On second thought, I was thinking I would leave the rear nearly flat, maybe some curved stiffeners behind it to prevent oil canning. Then maybe have light storage access, 20 cubic feet empty back there. Or, maybe a light pull-out galley on heavy duty drawer slides; as drawn the pullout outline is 40" off the ground, about right for a counter.