He's wrong!
Swagman brand carriers are designed specifically for RV's and I've been using one on the back of our TT for 8 or 9 years. They're very solid, in fact mine ripped my bumper nearly off but the rack remains solid.
The bad part is you must reinforce your existing bumper so it doesn't rotate downward under the force of the rack.
Have a welder add angle iron that starts under the frame and extends out under the bumper. This not only supports it but keeps the bumper from twisting downward. A piece that's 10~12" long works fine.