Oil base polyurethanes are fuel proof, however, they yellow in about 6 months. The yellowing is not too noticable on dark colors, but very noticable on light colors.

Water base polyurethane DOES NOT YELLOW, However, it is only fuel resistant.

The following caveats need to be followed with waterbase poly.

1. Let the poly dry for a minimum of 2 weeks before exposing to fuel/exhaust fumes.

2. Do not leat the residue remain on the finish over 4 hours - at ABOUT 4 hours the finish will begin to soften.

3. I have found that 2 or 3 thin coats (allowing 7 - 10 days between coats) is as good as fuel proof clear coat providing the caveats in #2 are followed.