Yankee-
have you tried alanon? it might be good to speak with people who understand...
and i'm wondering if it might be a good idea to get the car hauled out of your backyard? as there is some chance he'll move right back in when he gets out and then you'll have the same situation again.
there are other places for him to go...like the salvation army, for example...if the car is still there, it might be too easy for him to just take up residence again...if it is gone, he'll have to make another choice.
just an idea,
naive