I bought a package at an Arts and Crafts store of some "coating epoxy"; VERY thin, watery, and positively fuel/oil proof stuff; weighs nearly nothing. Coated the balsa belly pan floor with that, and it has held up very well. If you are REALLY, REALLY concerned with grams, spray hairspray on the balsa and let dry before putting on the epoxy. You will have a very well sealed and minimal epoxy base.