Being in the Caravan and Motorhome industry where it's more common for units being stolen, I've seen my share of security ideas and devices, but the best deterrent we know of is proper security posts that are fixed into the ground. Yes, a thief can still get through them, but as a visual deterrent, nothing seems to be better. (unless you have 2 posts)
I cannot imagine how unnerving it must be, knowing your pride and joy has been tampered with, and could be a potential target to be taken. We rarely see any vehicle crime in my area, but I know i'd be on edge if I heard it was going on near me, so I feel for you.