My local auto paint store is very helpful. They answer all my questions as best as they can. Just tell them that you want a semi gloss clear and a hardener.

Make sure that you wear a proper mask when spraying.

In the pics below, the blue Ryan is covered in Natural Solartex, and painted with auto paint, using a hardener. The red Luscombe's wings are Natural Solartex, painted with Rustoleum aerosol can, and Minwax Polyurethane clear coat.