if you spray color over old paint and bare metal, your going to see it. Are you using rattle can paint? best thing i can tell you, follow whatever paint manufacturer's instructions for the particular paint your using. adn use degreaser.
There is an epoxy primer in a can, but it ain't nothing like catalyzed epoxy primer..... so i guess i want to know what kind of paint your using before i get into more detail.
might i suggest you check out the body section at
www.hotrodders.com .....