Most Rustoleum...or Ace, or Krylon Enamels are fairly fuel proof ONCE fully cured... 7 to 10 days
The metallic and clears in rattle cans are not very fuel proof
Min wax Oil and water based Poluy urethanes are fairly fuel proof again once fully cured
I have a few profile stunt planes with Mono kote type covered wings and Red/or Black/or Blue Rustoleum Fuselages and tails....10 to 25% nitro fuels do not faze them any
I do not add weight with clear coats on the Rustoleum painted parts... with proper balsa / ply prep, filling, DC 540 primer (sanded, auto spot putty) I lay down one or two coats semi dry... after the recommended wait lay on one --Maybe two ---heavy coats... the final finish is shiny enough for me
Sport fly.... 3 yard stand off judging BY ME...grin