X chocks are NOT intended to be used as substitutes for wedge chocks when hitching or unhitching. The manufacturer is very clear on this issue - and states emphatically that X chocks should be removed BEFORE raising or lowering the hitch. For that reason, I use them in pairs only to eliminate about 75% of wiggle AFTER the trailer is fully set up and leveled. On a grade, if you only have an X chock to keep the trailer from rolling as you unhitch, it is very possible that the X chock will pop off under rolling pressure. I have seen it happen in a CG, and the trailer began rolling down the hill, stopped only when the jack post fell into a hole. Always use wedge chocks, IMHO.
2003 Ford F-350 V-10 Crew Cab 4WD Long Bed
2004 Jayco Designer Medallion 29 RLTS 5th wheel
Bill, Gayle, and Mindi (dachshund)
Retired at last !
Nothing is foolproof to a sufficiently talented fool.