Been hauling campers around since 75' and never had a break in or anything stolen...not saying it can't or won't happen, but odd's are, it would happen when you're not there. If alarm goes off and/or lights flash...guess it depends on where you're camping as to if it'll stop a thief or not.
We purchased land and developed a campsite where there is "kinda" easy access and 5 other's that own a 1/2 acre each in same area....will park 5er there at times for a month or longer, never have had anything go missing, nor seen any attempt to break in.....Guess I'm lucky too.
When we're camping, but away from our camper, Our two Boxers could be a pretty good deterrent....If trying to break in while I'm there, we have dog's and other means of defense:)