While we don't have a 5th wheel, our Rockwood Ultra-lite wiggled quite a bit at the back. Rather then spending the money on a set of Stailizing bars I spent $45.00 at Home depot for 3each 4' pieces of pre-drilled galvinized angle bar stock, and 4 each 4" strap hinges. I used 2 of the 4' section across the back of the trl with hinges bolted to each end of each bar. One hinge bolted to the bottom of the rear jack and the other hinge bolted where the other jack bolted to the body. Using right sized bolts to secure the 2 bars together. Once the jack is lowered I rebolt the 2 bars together. The 3rd 4' piece I cut in 2, did the same thing but used it for a front to rear brace.
2012 Winnebago "Journey To Insanity" 40U
2008 Dakota Sport 4x4
2004 Subaru Baja - DW's
2006 Honda Shadow Aero - TOAD for now.