You can put a lock on your hitch, but the odds are better that you'll lose the keys than a bad guy will try to steel the trailer. I used to use a locking pin on mine and I left the keys at home one time. I was amazed that it only took one gentle whack with a hammer to bust it off.
Just go camp and do your best to avoid leaving attractive valuables around camp.
Also FWIW, the only time we've had any theft was at our storage yard. Someone stole our cruddy old batteries. I was mad, but I knew it was time to replace them anyway.