One caution or caveat. I built a rolling platform that covered the whole bottom of the camper. I used 6" PNEUMATIC tires because my driveway is gravel/dirt. The resistance of the tires on dirt is pretty substantial. The U shaped mounts that connects the tires to the wood frame you bolt to the frame are bending. Moving the thing was pretty anxiety producing.
Also, I haven't moved the platform/camper in over a year and the tires deflated. I'll need to put the jacks back on the camper and raise it, and reattach the tires to their rims and inflate them. I looked a lot of places and if you want to move things around on dirt and gravel, it seems better to have a couple axles and bigger tires.
Just a thought or two...
Jeff