For a clear coat I can highly recommend a WATER BASE polyurethane. It is compatible with just about everything, it WILL NOT YELLOW with age, it is definitely fuel proof to 10% nitro (all I use) and various reports indicate no problems with 15% nitro, there are no fumes, soap and water clean up, and if you don't have spray equipment, MinWax has it in spray cans.
Most water based wrethanes are NOT fuel proof. They are a great under layer product. any of the oil based urethanes will work but they are heavy and will yelloy some of the colors.
Water base poly-urethane did not work out for me. After curing I applied some 10% glow fuel and it got sticky-gooey. Would not work for me as a fuel proof top coat.
OK, now. Seems we have a difference of opinion here. Iwannafly seems to be the voice of experience, but what brand did you try? Over what material? How long of a cure time?
Campy, have you tried waterbased poly U? What brand? Did you do the 15% test yourself?
Thanks for any clarification.
Phil
PS, I have tested and used white and two shades of blue Rustoleum and found them fuelproof, except that the white does absorb the pink color of 10% Omega fuel where the exhaust from my two-stroke directly hits it.