My preference when pre-treating with a glue/water mix is to use Elmer's Carpenter's glue.

Yo can thin it as far as 70% water 30% glue and get good results. You can paint it on with a foam type brush or a soft bristle (most house-paint brushes are too coarse) or even spray it on by filling an old Windex bottle (or similar)

Just enough to dampen the wood's outer surface is plenty. If you soak the wood, you are adding excess weight.

I tend to only pre-treat in areas where extra fuel resistance is helpful... Around the nose to about 3 inches back, and then anyplace the exhast trail is expected to go. This reduces fuel soaking if the fuel seeps under the covering, and that's the main bennefit I've found from pre-treating like this.