I have used the Por15 on my Chevelle and Camaro. Personally, I think it is amazing, but prep is the major key. As Tony said the marine clean isn't all that but the metal prep is key. It's an acidic base that will etch the metal for adhesion. The prep stops rust and the paint completely seals the rust from the air which prevents it from rusting further. If your not contending with a rusted out frame not, save some coin and do the rattle can.
Here is a tip, for easy masking of your body mounts and brake lines, use tin foil. it allows you to wrap the part and no tape is needed. It is also good for odd shaped parts and conforms to any shape.