What are some of the best ways to fill weave in .56 weight per yard fiber glass mat? It is on a 1/5th scale P 51 mustang and I'm concerned about the brittleness of nitrate dope for filler. Does caster oil really solve this problem? Products I've had mentioned are DAP lightweight, Hobbico balsa filler and talk added to dope, can't even find any pure talcum powder. Need help.