On my last camping trip just a couple of weeks ago, I had my camper slip and roll a few inches while disconnecting from my ball. I later determined that the root cause was twofold:
1) I hadn't lubed my ball / receiver in a few trips and it was not letting go as easily.
2) I had put on the wheel stop chock that I use
on one side of the camper but hadn't tightened it fully. When the ball released with the snap, it just twisted the chock to the side.
I was on leveling blocks on one side and the back blocks actually stopped the trailer from rolling. My biggest issue was that my tongue jack slipped off the board and buried itself in the ground.
As a result:
1) I lubed the ball and now have it on my pre-departure checklist to do/check every time.
2) I will tighten the wheel stop chock that I have tighter.
3) I have purchased and will use a second one for the other side.
4) I purchased a set of wheel chocks to slip under the tires
on the side that isn't being leveled. Steps 3-4 should give me three points of failure versus the previous setup which had a single point of failure.
5) I'm also going to use the tip above about keeping my chains attached until everything is disconnected and secure. While the chains wouldn't have helped there, the fact is that if my trailer had rolled further, it would have rolled right into the electrical pedastal that was about 4' behind my trailer. That would not have been pretty.