Hopefully you also made a police report about the incident. While they may not be able to do much, you will have at least alerted them to problems in that area. You mentioned that there were also a couple boats parked in the lot. Were they tampered with too?
I am fortunate here in the Kalamazoo area to be able to park next to my house. So far we have had no problems. I leave mine plugged in to a 30 amp circuit. I am more fearful that some idiot will decide to steal the 30 amp cord for the copper content. We have had a problem with bike thieves last summer. They would scan the neighborhood looking for open garages and walk up and ride away on their new bike.
What area of Michigan are you in?