Please excuse me if I seem a little obsessive/compulsive on this, but I had a real scare on one of my first times out.
I had always been on real level ground on my other TWO set ups, and didn't properly appreciate how little grade would get that thing rolling. I unhooked in a National Park, after unhooking my safety chains, without setting any chocks, and my TT went 'TWANG' as it came off the hitch, and proceeded to roll.
I bet I looked funny trying to hold on to nearly 5000# rolling along. If I had a shot of my face, I'd probably use it for my avatar.
The angels takes care of children and idiots. In this case, probably campground planners, as there was a bar of cement bolted at the down hill side, and my trailer wasn't going fast enough (yet) to jump it.
I've been a leveling, chocking fanatic ever since.