Start here:
https://www.southernpolyurethanes.com/ Their product is good and cost effective. Especially the epoxy primer. Read the product sheets. That goes for any manufacturer. They usually tell you what is best when using their product and sometimes, what you should use on it afterword. At the very least, you can coat you truck in an epoxy primer and leave it for a while to give you time to do other work and so you can decide what kind of finish you want to do. That seems to be what I'm doing on my Suburban. Removing rust and painting a section at a time. This month? The roof. Pictures in my signature link.
