I would avoid the POR15 and use a different/similar product - I will be using this stuff when I get to that point.
www.nomorerust.com - you can then top coat it with whatever you like including their chassis paint or their UV stable paint.
A LOT cheaper than POR15 and a LOT less prep. Very little surface prep and then you can spray it at no less than 10% reduction.
Check out some pix of the process in the build thread from msgross [Money Pit] - the coating stuff starts on page 2 - I have linked directly below
http://67-72chevytrucks.com/vboard/s...=242910&page=2
That [silver rust coating] is the stuff on my Blazer psgr side floor pan right now and it was in the elements for awhile and the water pooled on top of it.
I will be doing all the metal work on my truck then spraying it with the masterseries permanent rust sealer then doing my body work over that...should keep it clean for years to come.
Just a thought.