I talked on the phone with eastwood for over an hour and came to the conclusion that por15 would be very good but is a PITA to install since you have to brush it on. Eastwood is a por15 dealer too. I used 4 cans of their internal frame paint, 6 cans of rust encapsulator, and about 6 cans of extreme chassis. Also used half a bottle of PRE their prep chemical. All the products were amazing.
Check my build thread for more info and photos:
Gotopless Build