I think if you can, you should put the mothballs in your garage and one or two in the engine bay and park it outside overnight, he might be repelled by the smell and find other refuge.
If that doesn't work, I think the best way with the snap trap is to get a piece of chicken as bait, and tie it on to the trap with some string or wire or something like that. When the fucker goes to get it out it wont be a grab and run situation. He'll fight the trap, but it will kick his ass.
