They are just telling you to mix up a batch of epoxy then using 91 percent alcohol {bought at any drug store} and you thin the mixed epoxy with the alcohol so it is runny then coat the inside and outside of the fire wall with it. Then you coat the fuel tank compartment. I fuel proof from the wing bay forward. The reason for it is the fuel tanks or lines can leak and a glow engine sprays out a bit of fuel mist when running and the oil will soak into the wood softening it and softening the glues holding the plane together. It isn't near as bad with a gas powered plane. Some fuel tanks are better then others too and if they aren't assembled correctly the bung can come loose flooding the tank compartment.
Most hobby shops sell fuel proof paint but it isn't really designed to stand up to straight fuel. More just the burnt exhaust. Some people like to just use straight finishing epoxy instead of thinning 30 minute epoxy. How you fuel proof is up to you but it's well worth doing. I think it is Top Flight paint that is fuel proof up to 15%? I thin 30 minute epoxy and use that.