If you are concerned about warpage, you may want to try polyurethane. The oil based poly does not warp balsa, so no sealing is required.
I'm in the process of glassing a 121" Luscombe, using polyurethane and .5 oz glass cloth. This is my second usage of the products and I am pleased with the results.
In the first pic, the fuselage is glassed with polyurethane and .5 oz cloth. The second pic is a completed model that was glassed with polyurethane and cloth>