I usually fuel-proof with thinned epoxy before covering then if it is a open cowl plane (I hate seeing bare wood on my plane) I buy a little jar of Testors Model Magic paint the is a close match to my covering color, they have so many colors the are bound to have one that matches your covering. Then I paint the firewall or other exposed areas the paint is a epoxy enamel so and it seem fuel proof but I have always put it on over other fuel-proofing just in case.