If I were designing custom
I would lower the height of the side boxes to the lowest, nothing over the wheels, maybe even lower, have a 3-4" squared-off bump-up over the wheels.
Then go also as low as possible for the central floor, custom for that truck.
Now another way to look at it, call that level out to a full width "flatbed" perimeter, with that squared-off bump-up over the wheels.
And hang your storage boxes underneath make them as wide and low and lightweight as possible.
Then design and fab your removable living pod to slide right in there, fully supported by the central floor as well as the perimeter edge.
With the camper pod left behind, a fifth-wheel or gooseneck hitch, high enough for clearance, in order to leave the utility boxen in place while towing.
In my case need 17,000 pounds safe towing capacity, so a 450/4500 base platform, up to maybe 750/7500 and I guess likely a dually?