First think about what you want.
If you'd be willing to store the car for $50 a month, say so.
If you are not willing to store the car, say so.
It does take two people to have a fight, so don't justify, don't explain, just say it doesn't work for you and he will need to find another place to store the car. (It helps to tell someone what they need to do instead).
If you are afraid he may yell or fuss while picking up his stuff, invite over a couple of friends and ignore him/leave if he gets loud.
Also, this is getting a little bit pop-pysch, but it sounds like he is still trying to keep some claim/attachment to you by removing his furniture and leaving a car.