Few enamels (Rustoleum is an acrylic enamel) are fuel resistant at all unless they have an additive of some kind to make them be. As for fixing your plane, you could top coat the rustoleum clear with a 2 part clear like the Klass Kote, but you'd obviously be adding more weight. Maybe if you only added a fuel proof clear to the places the exhaust hits the worst you'd be ok.