Before my very ugly falling out with them, I used to work in a RV dealer parts department. We had a very irate customer who came in one day. He had purchased a bike rack that clamped to the square tube rear bumper of the new camper he had recently purchased from us. He was taking a trip and stopped at a rest area. He found that all three of their bikes were missing, the bike rack was less vertical and more sticking straight back to the rear and the rear square tube bumper was twisted like a corkscrew. He was talking to the manager and was pushing for repairs to his camper as well as replacement of the bikes.
To make this story shorter, the rear bumper was fixed under the camper warranty and he was cautioned that since the tube wall thickness was so thin, doing it again wasn't advisable. Soon afterwards the RV manufacturer (Starcraft) sent out a service dept. notice advising that warranty claims would not be honored for rear tube bumpers where any non-factory items were mounted on the tube bumper.
So unless the tube bumper is made of some pretty beefy material, don't do it.
FAA A&P mechanic, ex-RV dealer parts dept
Retired B-52 Gunner/Flight Examiner, B-52 Crew Chief
2016 Jayco Eagle HT 29.5 FBDS w/ 15,000 BTU AC, 50 amp service, upgraded counter top, thermal pane windows, elec. stab jacks, outside grill, backup camera and MORryde pin box.
2011 GMC 2500HD DURAMAX/ ALLISON