I use epoxy as well, but I prefer to use heat to thin it with. Use 30-45 minute epoxy and place some on the area you are fuelproofing, and hit it with your heat gun. It will thin down to the consitency of water and you can easily brush it in place. I prefer to use the heat because it doesn't change the chemical breakdown of the epoxy. Using a thinner it is possible that you can change the epoxy to the point that it will never set and you'll wind up with a gooey mess that will need to be scraped off and you'll have to start over. Yes, I know that many use thinners with no problems and I have done so in the past. But like I said, it's possible to mess up the epoxy. Plus, using heat you can get the epoxy to a thinner state that will allow the epoxy to be easier to spread and will soak deeper into the wood which will improve the fuelproofing of the area you are working on.

Hope this helps

Ken