I have a FW24F with full wall slide and have a bit different solution that works for me.
I cut three lengths of 1 inch PVC and put threaded couplings on the ends. The lengths are cut so they fit in my cargo bay and when put together they extend 6 inches beyond the end of the topper both front and back. I ran shock cord down the inside of the PVC. When the slide is extended I place the assembled tubing over the top of the topper and bungie the cord ends under the slide. Be careful not to make the bungie too tight. I put enough tension on to keep the topper from flapping. I sleep like a baby at night.
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