generator on rear bumper cargo rack

As has been said, the square tube "bumpers" (even calling them that is a stretch) on most RVs are only adequate for carrying the stinky slinky. Using a bolt-on receiver to mount anything is a recipe for disaster. Between the leverage from the rack and cargo (even bikes) and the amplified G-forces at the back of the trailer, the welds at either end of the bumper will fail in short order. I could probably find dozens - if not hundreds - of images of this happening with a quick Google search. The only safe way to do it would be to have a qualified fabricator build you a receiver and/or rack that is welded to the trailer frame itself.

Rob