They will give you an additional parking sign/paper upon checkin to put on your dashboard for your extra vehicles. I have also seen people get one (that are there for extended periods of time) get another one and put it in a ziplock bag and tape it to their boat/trailer that is in the overflow lot. As long as you let them know what is going on at check in, they will give you the necessary paperwork to keep it there and out of harm's way. We keep our golf cart trailer in the overflow lot when we stay. We put a trailer lock on it (because it can be hand carted off) and we have never had a problem.