It appears the tire mount was glued to the fiberglass and may be bolted through the rear wall as far as I could tell. When we had the spare replaced the tire guy had trouble getting the tire off and the plate came away from the RV a bit so I had to caulk it on and caulk the edge before remounting the tire at home. I didn't take photos so my memory is foggy but I don't think it came off more than a little bit because of the bolts. Anyway it is convenient.
Also I ruined the bumper mounting by partially attaching the second set of heavy duty rollers onto it. (The first set fell off on a bumpy road.) When they hit the ground, they pushed up the bumper. But I figure that is better than hitting that rear end again or tearing up our steps again. :)