The first Brownells Gunsmith Kinks book had instructions on how to thin original Acraglas and spray it for a stock finish. Never tried it but it sounds like it would be a sure fire waterproof finish. Since Harbor Freight has cheap alr brushes I am tempted to try it and just throw the sprayer away when through.
Another option would be clear Duracoat.
Whatever you use, a heavy coat of paste wax adds another layer of waterproofing.
That does sound like an excellent and durable finish. There are some boat builders that brush on epoxy coatings for a similar effect; my dad used that on the boat he built but I don't know what brand.
