You aren't the first person who's done that... built a custom bed that will accept a normal camper and allow for big side boxes. Cool idea anyway.
It has actually been done quite a bit, but not like this, at least that I’ve ever seen. I’ve looked at a LOT of deck/box combos.
A flatbed deck sits 5” higher than a standard bed to allow for rear wheel articulation. That raises the camper 5” higher than it would be in a standard truck bed. Highway Products does it this way and fills in the gaps under the sides of a slide in with upper boxes.
Sherptek takes this a step further by offering a low, standard bed height, completely flat deck. They notch out for the rear wheels and build wells that go up inside the upper boxes to allow for articulation.
The Bowen deck takes this yet a step further. It won’t be flat. The middle will be at standard bed height, but the sides of the bed will be 5 or so inches higher. That way the slide in camper will ride at standard height, but the wheels will fully articulate without having to intrude into the upper boxes.
It’s a new concept as far as I can tell.