INO you now have to fix an ut-oh , like the Idea of of the POR-15 that is the type of repair it is designed for (paint over rust). again IMO the process should be reach as far as you can with wire brush and wire brush the inside of the cowl ,blow it out with air, then wire your brush on to a sturdy but flexible rod (round) plastic dowl usually sold in hardware stores) and get to deep hard to reach areas and again blow it out. POR-15 is made to paint over rust so its not like painting the outside of a car,.now a little pre accident thinking and planning. mask off your cowl to firewall seam really well,POR-15 is thin and runs really easy, do not want it to run threw you seam and all over your pain.(if it does wipe it immediately with prep clean ) make sure you use gloves and long sleeve shirt and i would paint with a foam brushput on 2 coats read instructions first ,i think its `1/2 hour between coats. i also recomend to have the color of your engine compartment handy and paint it on about 15 to 20 minutes after second coat that way it will make a chemical bond to the POR-15.