I am running the Show Chrome non BRP trailer hitch on my RS. After pulling my Time Out trailer to California and back I found a very disquieting problem; the hitch was moving up and down on the swing arm pivot point!! There is a 8mm allen head set screw in the bottom of the side pieces that mount over the axle nut. This set screw is a pointed end that contacts the swing arm. I had tightened these as much as I could twist with a 4mm T-handled allen wrench before leaving and again in California as I had to remove the hitch to replace the rear tire.
After returning home I attended a Mi. Spyder riders meeting and mentioned this problem to a member that had a identical hitch. His recommendation was to replace the allen head set screws with a conventional head bolt that was flat on the bottom; so I did this and after just returning from the UP trip, the hitch remains solidly in place.

SOOOOO my recommendation to others is if you use the aftermarket hitch on your bike to replace the pointy ended allen head set screws with a flat bottomed conventional wrench head 8mm bolt.

And I'm sorry to report that I can't remember this gentleman's name, but he and his spouse were riding an 2015 RT. Thanks again for a great solution to this issue.