RE: Glassing 1/7th scale P-51
All your really doing is sealing the balsa so you can paint and not read the balsa grain later. One ply of 3/4" along with Z-poxy will not keep you from damaging things from handling errors, and heavier cloths will add too much weight to fly worth keeping, so do yourself a favor and forget about using any kind of polyester or epoxy resin, keep it light and get yourself a can of Minwax polyurethane from Lowe's or Home Depot, place the 3/4" cloth down and brush on the Minwax, allow to dry, scuff sand with 320 grit, brush another coat Minwax repeated by sanding and your ready to start priming. This is simple, light, and the most cost effective way to prep for finish. measure length X width of everything and divide by 144, this will give you your SQ. FT. area of cloth to purchase.