I'm sure you all plan to put $10k paint on your show queens, but my beater panel is a work truck. Tony: Two cases of Rustoleum bare metal primer covered the entire truck, inside and out. The fenderwells got a dose of ZR and then brush-on undercoating. The fenders, doors, etc. were painted in the shop to minimize moisture leeching into the primer; this was a problem with the body. I tossed a massive blue-tarp over the truck when it rained and I still had to do spot-work on the roof when condensation got under the tarp. The body didn't fit inside the shop, so we slapped a topcoat on it the first chance we got.
ZeroRust is great stuff, but pricey compared to Rustoleum primer. If I were to leave a truck in primer for a year, ZR is what I would choose. BTW, Rustoleum green seems to stick to ZR just as well as to Rustoleum metal primer, your choice of topcoat may have different results.