I have several of the Toppeak beam racks. I hate them. No matter how tight you get them they still swivel on the seat post.

I also have some of the Arkel Randonneur racks and highly recommend them. This would be just about perfect for the application and these are very sturdy and stable. Arkel also has a Tailrider pack that would work perfectly for your application. The three point connection to your seat rails and your seat post make for a very stable rack. In addition, it is quickly removed (seconds) and/or reinstalled. The picture below shows the extenders that go from the seat to the rack. These can be removed as well, bringing the rack higher up.

We have replaced all our Topeak racks with these. Huge improvement.






J.