Not familure with your particular slide but I can tell you what Schwintec recommends.
Cut a 2x4 so that it will wedge between the top lip of the slide and the inside wall. This will prevent it from sliding back out.
Paul, Kathy, and Tux the Mini Schnauzer
2014 Tiffin Phaeton 42 LH, 2013 Honda CRV
"When the time comes to look back, make sure you'll like what you see"