I had a rack built that sits on the trailer tongue above the propane bottles, that holds my Champion 2400.
For a rear mounting of another rack, I had the tinfoil bumper removed, and a heavier four inch bumper installed, then I welded a receiver to the bumper and frame. (After that, one could mount any type of rack in the receiver.) I have a rack that is as long as the travel trailer is wide that mounts in that receiver, and also U-bolts to the ends of the heavy-duty bumper to stabilize it.
Any thing that you mount onto the rear bumper will need to be well thought out, because that cheap bumper an RV comes with won't hold safely much more than a spare tire rack.