Needs to talk to a surveyor. I suspect this is more about a land grab then it is about military vehicles. Truth is, law says if you live on a property, and put a clothesline across the neighbors yard adjoining yours, you can make a claim on that property where your "improvement" is after a period of about seven years. Varies in different states, but law is always funny when you get into these things. And the point of all this hoopla is, get your stuff off that property else you might be able to claim it as well.
He getting some free property is a whole lot more important then anything in particular sitting on it, but the longer you leave it there, the more difficult the battle he might have to fight in order to make a legal claim on it. And since he beat you to it, it is going to cost you nothing but money to get anything you might want out of it at this point. He has the upper hand. I would be careful where you go with this one at this point. It could cost you a whole lot more then a MV displacement.
Realtors are not responsible for accuracy in property lines or disputes. Nor are they liable. They just sell property. They don't have to define the exacting lines, and often sell property without known boundaries. It is the responsibility of the buyer and his finance institution to define the lines accurately as to what they are buying and what they own. Even the seller does not have to define the exacting lines. I've known people who purchased a new house built half on someone elses property. OUCH!