For fuel proofer use BalsaRite for film. I put some on 2 pieces of balsa. Then I put the sticks into a baby food bottle full of 15 percent fuel. Closed the lid. Opened the jar 2 weeks later and broke the sticks. They were perfectly dry and snapped as they should have.
Been using it ever since. I also use it over dope if I want a colored look. Works great!