What I found, when searching for the right utility bed for our project, is the one you want is the shorter ones. Lower profile, with no tray on top. As utility beds go, they tend to be the lighter ones anyway as they are just smaller.
As for mounting to the frame, we pulled it off an F-250, where it had been since '74, installed it on the F-350 the same way it was. Don't really see how one could mess that part up.
The beauty of our camper is we mashed it together from parts gathered up cheaply. We have less than $25k in it. Dreamed of an Earthroamer, or some other pricey camper. No way we could afford it.