How about a cube/box van body on a cab/chassis truck?
It's like a class C motorhome, but not on a van chassis, so you can have crew cab, diesel, 4wd, high ground clearance and heavy towing capacity, like a truck camper, but you also have cab to camper direct access like you want.
A U-Haul/Ryder/etc delivery truck could easily be built into a nice RV inside the cargo box, if 4wd isn't important. Look for an ambulance truck from a northern state, if you want 4wd.
If you find a refrigerated delivery box truck, all the better, the box will be super insulated and have an awesome self-powered A/C unit already built in! You could take the box off the truck, if you don't like the truck, and put it on a cab/chassis truck you do like.
Here's another idea. Buy a cab/chassis truck that has the configuration you like (cab size, 4wd/2wd, diesel/gas, frame length), take whatever bed is on it off, find a small travel trailer, like a 13' Casita/Scamp/etc, remove the axle and tongue, and mount it to the truck chassis. The RV part is already built by using an existing camp trailer.