I tested Minwax Brand "Fast-Drying POLYURETHANE Superior Durability". It comes in rattle-cans in gloss, semi and satin and is pretty cheap too. I tested it on some panels and it sprays very smoothly. After it cured 48 hours it was impervious to raw glow fuel even after being left on it for a couple of hours. The only problem is that it takes a long time to dry despite what the label says. I haven't done any long term UV exposure tests so I don't know how bad is bad but I'd stay away from whites and other light colors because of that yellowing problem Campy mentioned.

I also tested Minwax Spar Urethane and its fuelproof too but they tint it to give wood a golden hue. It looks great on wooden interplane struts and stuff, but white fabric - not so nice.

As always I would recommend you try each paint and clear together on test panels for reaction with one another as well as fuel before doing anything on your airplane.