MJD, did you just say that nitrocellulose dope can be improved with urethane hardener..? I'd like to do some tests if that is feasible.
PS, I've had WBPU turn to gooo with light exposure to fuel spray [after reading at RCU that it works just fine]. Is the Spar Urethane oil based..?
There is a poster at RCU named Sensei who raves about using oil based poly urethane to apply lightweight cloth to balsa. I'd like to know more about that, but I'd like to think that every layer of the finishing system is reasonably fuel proof and not just the top coat.