We had a professional welder attach a hitch to our 2012 HT 26.5RLS early in 2012 before towing anything. He reinforced the I-Beams about 4-6' from the rear toward the axles and then fabricated a hitch from 3-4" square tubing. The total job took him about four hours from start to finish and included wiring a seven-pin plug as well. We tow a Crestliner SuperHawk 1900 behind the FW and have had no problems. I would be very hesitant to bolt on a receiver hitch to tow something as heavy as our boat, but for putting on bike racks, it would probably work ok. As far as warranty, the manual does say that attaching a hitch will void the warranty, but they are now attaching a hitch as an option, I believe, on the HT line. So, I wonder what changed now compared to when I bought my 2012? Send me a private message with your email and I'll send you some pictures of my hitch work. The cost for the fabricated hitch was right at $500, which I feel was money well spent.
2012 GMC 2500HD D/A Crewcab
2012 Jayco Eagle SuperLite HT 26.5 RLS
2009 Crestliner Superhawk 1900
2013 Polaris Sportsman 550 EXP
2008 Polaris Sportsman 700 X2