To really fuel proof the firewall, I suggest this; Mix whichever epoxy you wish to use and brush or glob it over the bare wood. THEN take your "money-kote" heat gun and start blowing the fuel proof aera with fairly warm to hot air.

The epoxy will run GIN-THIN all over. Stop and brush around. Try this several times until you are satisfied with the job. The hot epoxy will soak into the wood, every little slit, crack, etc and you will wind up with a fine fuel-proofing. If you need to paint, don't use dope over epoxy. It will lift off as it shrinks so much. Poly urethane generally works fairly well.

Now, in all these years I never ever thought about painting first. You may be on to something here. I will try that as soon as I get a round-to-it! [8D]

Good luck.