Locks in general only keep honest people honest. About the only way to really ensure somebody doesn't drive away with your trailer is weld it to anchors in the ground. And even then, they could always cut those off with a cutting torch.
The coupler lock I use is easily defeated by just using a smaller size ball. But I'm not worried about it. It's parked in a gated storage facility, and it has cameras, so there's going to be some logs about who comes and goes. Not that that'll help if somebody did drive off with the camper. The insurance takes care of that.
Speaking of the storage lot. I do see some people using boots (like the ones parking enforcement use) on some of the cars stored on the lot. The funny thing is, those cars are often old junkers barely worth the steel they contain. Come on, you're really worried about somebody driving away with your '88 caprice that's missing a door and has a 1/2 caved in roof? Or that '84 reliant with no interior?
There's no use crying over spilled milk, unless it's on your keyboard.