All kinds of things can happen outside your RV, especially at truck stops, rest areas, Walmarts, etc. The thing is who cares as long as they don't mess with your rig. If it is just noise you are worried about, there is not much you can do, with or without a camera. If someone makes noise or are wandering around your coach at a truck stop, and you see them on a camera, what can you do if they haven't touched your coach?
Some people carry a firearm and you are allowed to protect yourself from a home invasion. You can't go out and shoot someone just because they disturb your sleep.
The best choice is to find a nice quiet RV park and even then a noisy neighbor can pull in next to you. :B