No first hand experience because I had just read too many negative things about frame flex when we had our Aliner and 23 foot TT. I know in the Aliner world there were folks who reinforced their frames in order to throw blike on the back bumper. Personally, I wouldn't do it.
Kristin, if you don't mind I will take the other side of this discussion.
PJ, I bought a 2014 Aliner. When I was on the dealer's lot, I was disappointed that none of the models had the 2 inch hitch receiver on the rear that previous models had had. When I asked the dealer about it, he said the hitch had been removed after the 2013 model year because customers had dragged bike racks or carry racks (carrying generators for example) when people took their Aliners off road. It wasn't Aliners' fault but they were tired of dealing with it.
So the dealer offered to put a bike hitch receiver on the back and I took him up on it. However, I had it welded back to the frame on either side and not on the back bumper. Most back bumpers are sheet metal stamped in a capital letter C (backward) shape which won't hold squat. I would not trust those one lick.
Even with my rear receiver, I still have to be careful. Adding a couple bikes and a holder cantilevered off the rear means I need to add enough weight IN FRONT of the axle to counteract the loss of tongue weight. Normally my trailer should have about 200# on the hitch but if I add 200# in the rear, I could be in trouble. It's a Moment Equation around a center of rotation so to speak. All the while still being aware of the cargo load I can carry in my trailer, the tongue weight, the GVWR, and such.
I am not that worried about voiding my warranty since they are two years at most to the original owner (I will have 2 years in April 2016). I tow my Aliner with a Suburban so there is no truck bed to put bikes in and I am past the point of trying to hoist them on top of the tow vehicle and down at our destination. And visa versa going home.
Bottom line is I wouldn't put a rack on a sheet metal bumper. Up to you if you want to have one welded to the frame. But all the rules about warranties, weights, balance, and towing apply. We love taking our bikes with us when camping (especially at the Fort) so this is what I was willing to do.
Bama Ed
PS - EDIT: for PJ or anyone else, not all trailers can used a welded receiver to the frame approach. One of the things manufacturers do to make the trailers lighter is to use a lightweight frame which would be unsuitable for the high heat used in welding the steel crossbar. Attempting to do so might do more harm than good....
