Has anyone tried using laquer based polyurethane to do fuelproofing in the tank compartment and around the firewall?

Is this stuff fuelproof?

I'm wondering because I'm using Deft poly-u to 'glass my whole TF Spitfire, and it'd be easy to just slather it on the firewall area while I'm glassing.

I've also heard from a few people that epoxy isn't as fuelproof as people think. I myself have experienced epoxy failure in the firewall of my GP .40 Mustang.

Thanks!

-Joe