The mixture in the fuel compartment makes the fuel not soak into the wood. The covering on the tail does the same thing but at a much less weight factor. You can prime and paint the tail, and it will do the same thing. Adding epoxy over the top does nothing but add weight.

I would re-think it if I were you. It is really pointless and you will screw up a good plane. Every ounce of weight you add to the tail, you have to add about two to the nose to counter it because the arm is longer to the tail from the CG.

They guys had you do the tank compartment, because that needs to be done along with the firewall. Doing it to the tail is not good. Let the paint or covering do that. Anything else is just extra weight.