The
weight of the shell itself would be likely be fine on a small pickup truck. But then you start adding stuff into it such as window glass, cabinets, cushions, mattress, appliances, water in the tanks. Along with clothes, food, tools, toys, various other entertainments such as a TV and it will be overloaded. But over the years people have found salvaged dually axles to put onto small 6 cylinder trucks and done a transplant that had enough power to keep it up to a reasonable speed on the freeways.
With the regular motorhome Sunraders you also have to carefully plan out the distance to the wheel well so that the wheels end up in the right spot on the fiberglass shell and also fit into that space size wise. I believe they also extended the frames as well as changing the axles on the Sunraders to make it work. A lot of factors to think about and lots of work to make it happen but it has been done more than a few times as it is a nice strong shell... if you don't rip the foam off of the ceiling in which case it will sag down.