The usual advice is that the factory rear bumper (4" square) is not attached adequately to support any kind of weight that withstands the rigors of travel. Bumper attachment to the frame would need to be reinforced by a welder. I have never done this, this is just what I've read online. The RV dealer did tell me that if I wanted to mount a something on my rear TT bumper (standard 4" square) to store a generator, then it would need this kind of reinforcement to be reliable.
2012 Aspen Trail 2710BH | 280 watts of solar on the roof | 2x6V GC batteries | 100% LED lighting | 1500 & 300 watt PSW inverters | so far strictly boondocking