If your concern is strength then it will be hard to beat epoxy and glass. It is heavier but with good techinque not real bad. If weight is the main concern then I suggest poly, but I have not used it with glass yet. I build 20-30 pound planes and want a very hard surface and added strength. Clean your surface well before glassing and only put enough epoxy on to completely wet the glass. Remove access epoxy to save weight. Practice on something first.