I've been advised that Minwax indoor/outdoor Helmsman Spar Urethane, in a rattle can, is reasonably fuelproof and compatible with other paints/dopes; it can be used as a clear coat for the fuelproofing and shine. I have put it on a few planes this winter, but have not yet flown them--so I don't know just "how" fuelproof it is. There's been no issues with reacting to other paints; I've put it over Rustoleum mostly, and it looks good. that's all I can tell you about it right now.
--Ray