Hi, and welcome to the forums. I had this concern about our Sovereign
, it turned out the problem was really two problems. The first problem was that over the decades, the axles had sagged to the point we had a "low rider". The second problem was the edge of the floor had rotted all the way in the back, coupled with a sloppy previous repair, had caused the frame to sag.
The two together caused a back bumper that was only a few inches of the ground, and did drag at times. Dragging the back bumper is not a good thing, it can tweak the body, and cause other damage. If you put skid plates, or wheels, rollers, or whatever back there, it will make it even lower, and more susceptible to dragging, and damage.