We had a Monaco "semi-monocoque" body/chassis. The reason they called it that was that the "frame strength" was provided by a bridge type truss system in the walls of the body of the coach. While it didn't include all of the body, it did move the forces up into the lower 18" or so of the body.
Personally, if a motorhome has 3-4 slides, to say nothing of a full slide on one side, I do not believe that the monocoque either full or "semi" is as good as the rail coach. By the time you put all of those cutouts into a body, it is next to impossible to get the strength that we think of with monocoque.
Just my thoughts as a former strength of materials engineer. And I apologize because I dont' think I've spelled monocoque correctly.
Ed Headington