I purchased a vintage travel trailer from a private party who sells and refurbishes vintage trailers. I purchased the trailer to be restored by the same person. The person no longer has the money I paid him and the trailer has had zero work done on it. I want to get 100% of my money back. How can I do this?

You can or should get the money you paid them for the restore.
Since you actually received the vintage trailer the money you paid for it, may or may not be able to be received.

A lot will depend on the sales contract and written agreement to do the repair.

Of course after you sue him, if he does not have any money, ever actually getting the money is another issue.

If this is his business to restore trailers, what does he say about fixing it ?