Something like this, maybe....
That is so cool!
an intrinsically stable torsion free mounting specifically designed for the truck; built by a professional.
A single axis leveller (or getter outa bedder)
Depending where the toilet is you can empty it without even touching it (composting or waste tank)
You can have the over cab bed (SUCH a space saver) without compromising the cab tilt. Just be sure to have a hand or electric pump as backup; you're going to look silly if you can't tilt cos you're engine's kaput.
As long as you run all the lines to the back before going into the camper, it also makes it much easier to demount if you need to change truck, or live in during repairs.
I swear if my truck had come with a tipper mechanism I would have kept it.
Back to the OP: What do you care how much it cost to build; commercial bodybuilders are prohibitively expensive the moment it's a custom build.
I promise you it'll sell for about the same amount as you'll have to pay to have a torsion free subframe made up; if that.
It cost almost as much to remove my CRANE and flatbed as I got for them in the end.
Cut the sides off, cut away the sheet steel panels of the floor and you have the ideal subframe, torsion free and ready to build your box onto. Built by a pro, specifically for your truck; what more could you want?
Hell, if you go for welded steel frame don't even cut the floor plates out, just insulate onto them.
That's just what I'd do, others are allowed their ideas too.
