I lock mine when leaving camp. But before I had the A Frame, I had a Coleman tent trailer without a lock and never had anything stolen from inside. Locks are there to keep the casual, opportunistic thief out. The kind that think that if something isn't locked the owner doesn't care. That is what you are most likely to run into at a camp ground.
No camper will keep the desperate or intent thief out, so don't give them any reason to believe there is something to gain by breaking into your camper and the probability of trouble will be low.
