I have made them from wood, simply like a rolling pallet. I have also bolted 2x4's going up that the body bolted to so it was up at a more workable height. Sorry, no photos.
But we have a number of carts at work that we put pickup beds on I can snap a few photos tomorrow. At home I have one in the works but haven't even built it. What it is simply is a frame from a truck like mine (48 Chevy) that I cut off at the firewall and rear panel so the cab will bolt down just as it does on the frame and I have some nice large casters I will put under it. This way the cab can be worked on mounted to the "frame".