I fuel proof all my planes with epoxy thinned with denatured alcohol at about 50-50 and do it back as far as I think fuel would go if the tank ruptured. I use acid brushes because you can bend them at a 90 degree angle to get at hard to reach areas and wear disposable gloves. Let it dry overnight and it works great. Most hardware stores sell denatured alcohol cheap and while you are there get some acetone and lighter fluid.