I have tested various clear coats over the past several years.

I have found that water base polyurethane does not yellow, however is FUEL RESISTANT with the following caveats:

1. Let the poly dry for a minimum of 7 days before exposing to glow fuel (or residue).

2. Do not let the exhaust residue remain on the surface over 4 hours. After 4 hours the finish begins to soften. The amount of time it can be left on the finish may vary between brands. I tested Minwax Polycrylic.

If you can find it Ultracoat clear is fuel proof.

I have also had some promising results with Krylon ACRYLIC clear in the high gloss.