Try to make the camp appear (look & sound) to be occupied - lights/radio on timers - ON at night time, leave a junk car in the parking area. Timers are only a few bucks at Lowe's or Home Depot.

Spikes on / logs over the ATV trails, hide valuables in a secret area (trap door in the floor under carpeting or in the drop-ceiling), fake cameras, fake security sign, motion lights, good insurance.

If it snows, have one of the neighbors drive up to the parking area, just to leave a fresh set of tire tracks, so it looks like somebody has been there recently and may be coming back.

It's the little things that can deter trespassers/vandals from striking. Generally, these are cowardly individuals who shy away from confrontation. If there's even the slightest chance that they'll get nabbed, they'll find another target.