JohnD
Moved on to the next thing...
On our first travel trailer I used a pair of X chocks (not the extended version). For a test one day I set the chocks while hooked up to the truck. Put the truck in gear and just taking my foot off the brake was enough to have both chocks pop out. They really did nothing.
I do my pull test with my X-Chocks only and I don't have to pull the manual brake slider . . . the X-Chocks hold the Prowler in place.