I use polyurethane , its cheap, goes on easy and seems to work great as i had two leaking tanks on my eindecker, before Assembly just paint the firewall and inside the fuel tank compartment, on the eindecker it is very accessible before you put the cowling on. I have done four planes with a little can of it and still have lots left. It is fuel proof as my leaking tanks did no damage that i could tell and it wiped up ok, nice and dry wood. good luck to ya Butch in Niagara Falls NY