I don't know a thing about the primer that 76GMC1500 suggested - it may be great. Acrylic primer by itself will not protect steel. It is porous and the substrate(steel) WILL rust. If you plan on leaving your vehicle in primer for a while, like thru the winter, a properly prepared surface and epoxy are the only material that will do it. There are many brands of epoxy primers though the most economical that I have found are Nason (a DuPont sub-brand) and Southern Polyurethanes in Georgia. If you call these people, you will talk to the owner, Barry K and he will go thru the process and answer questions you didn't know you had http://www.southernpolyurethanes.com/homepage.htm

When you finally decide to paint the vehicle, scuff the epoxy with 180, hit with another coat of epoxy and start your process for paint.