Well this is what I used to do about 20 years ago. I had a welding shop and one of the things I built were truck racks. I painted all of my finished work with a high quality rust inhibative industrial primer and top coated with a high quality rust inhibative industrial enamel. I purchased both from the same paint store.
When I painted racks I would reduce the enamel with synthetic reducer and add some Dupont hardener. The results were very good. Very hard and shiny. With a nice finish.
