I yoosta drive a bread truck and always thought that would make a decent camper.
Nowadays I'm thinking more along the lines of something with less frontal area.
I do like the Sprinter based units.
Having used a very heavy and large pickup box camper and pondered a bit about improving fe without re-engineering the whole dang thing, I concluded that it is just a great lumbering ox and about all I can do is cruise at 50 mph as steadily as I can, where it gets 10-11 mpg.
There are many un-aero protrusions but even if they were all banished the barn-like frontal area and shape remain to ruin aero. It takes a fair amount of power just to move that thing down the road; I didn't get the impression that higher gears were a good option and of course an OD like a GearVendors unit simply doesn't pay for itself with the miles that camper accrues.