Campgrounds should be very safe to leave it.
Out west many people camp along BLM roads or just out in the middle of nowhere. That is a place to be concerned.
I have never unhooked in the desert and left my trailer. Im took scared, it is too easy for a thief to hook up and drive off, too few people around to see also. I have left the trailer hooked and locked to TV and left it though.
Insured, yes. Able to just write a check and continue the trip? never. Game over.
A better question is how safe is leaving a camper in the BLM type area?
(and I mean a nice trailer, not an old popup nobody wants to steal anyway, no offense)
Also, I theorize that a 5th wheeler would be safer as fewer thieves will be able to tow one, or be set up for 5th, and most who have a 5th hitch have enough money so are not petty thieves.
What security measures are best? Wheel locks, hitch locks, removable hitches???