Paint Inside Cowls and under dash

[hotrod1]

Like everyone else, my inside cowls and under dash is rusty. I plan on sealing up my outside air vents so this area should not get wet again. What have you used to paint these surfaces to make sure that they do not continue to rust. I thought about POR 15 but it seems like overkill because it will most likely never see water again and no wear. Tell me your opinions please.