I had the Rivco on my 05 Wing. It attached directly to the frame and not too bad an installation. The Kury and Add-On hitches only attach to the saddlebag framework, which, IMO, is not designed to handle the stress of that kind of load.

A hitch that attaches to the bike's frame is the only way to go. Rivco and Bushtec are the only ones that do that, to my knowledge. On a Wing forum, there is a trailer sub-forum with excellent info from smart people. Check it out.