When I first took over my park I had a sever problem with vandalism and the criminals breaking into trailers to cut out parts that could be resold for scrap. Once we cracked down on rules violations, let everyone know we were serious, and evicted the worst tenant the crime stopped. A few suggestions:
-Pass out a letter to everyone in the park letting them know to please contact the manager if they see anything suspicious, and that you will provide a cash reward to anyone who can give evidence that leads to the arrest of a vandal.
-Crack down on rules violations, your worst tenants are also probably your criminals.
-As an alternative to a real camera, you could post up notices that video surveillance is now in effect in the park, and then put up fake cameras that you can get for ~$10 off amazon.
I would try the above three first, and then move on to real cameras if those don’t work.