I looked at the Lippert Rack and it seems well designed to me. It had two mounting locations welded to the trailer frame and was made of heavy steel. When pinned in the upright position I don't see how you would be getting the movement you noticed on the Rigs your were following..
http://www.lci1.com/lci-storage-systems
I would recommend for anyone that has a receiver type rack that you consider a Hitch Vice by Hitch Rider. Stops all movement in the hitch.
http://www.hitchrider.com/nowobble.htm