We stay in COE parks and State Parks and have never had a theft. I think I was close Friday night when we overnighted at s TA Travel Plaza. DW said the next day she felt the trailer rock(no wind that night), but she didn't wake me up. I looked and the top was missing on my battery box. It could have blown off during the drive, because the tie-down strap was really cheesy. At any rate, when we get back, I'll go about making a metal locking strap to lock the battery box to the frame and make up cables to secure grill, chairs, etc to the trailer. It's a shame that we have to resort to that, but it is what it is.
I agree that the sophisticated thieves are going to carry basic tools like cable cutters and screwdrivers, but I think what we run into in the campgrounds are kids or someone looking for an easy grab, and the best way to make them move on is to make it hard fro them to steal. Most won't spend a lot of time trying to get something if they are going to risk waking someone up in the middle of the night.
The second best theft deterrent to the sound of a round going into the chamber of a pump shotgun is the one made by racking the slide on a 1911.