[chris vickery]

Why don't you guys ditch the POR15 and stick with epoxy primer?
The stuff is tough as nails and you have to grind, burn or blast it to get it off of properly prepared surfaces.
Metal should always be roughed up no matter the paint or primer product, unless you are using an etching primer.
Epoxy primer needs to be top coated within 24hrs otherwise it needs to be sanded before paint application, BUT, you can cheat a little bit if you epoxy prime first and top coat with regular primer. Most red oxide type primer can be painted over directly without the need for sanding and can be left for quite some time without worrying about it.
The epoxy primer provides the seal of the base metal while the regular primer acts as the bond for the paint.
You can also have epoxy tinted, I usually go red to simulate factory primer- if the paint gets scratched the primer will still protect the metal and looks original.