Lately I've been using Krylon Fusion as it's made expressly for plastics...then (as it's not fuel proof), top coating with with an automotive epoxy clear. Time will tell if it is a durable system. I like the spray nozzle and the way the product levels.

Some years ago a friend and I decided to experiment with an old beater he had been flying for years in order to determine which paint was best suited for aplication over MonoKote. It being a shoulder wing plane, we shot some color panels on the top of the wing immediately behind the engine. If memory serves we shot a patch of Krylon, formula U, Rustoleum and another brand which I can't remeber. After a summer of flying and much abuse, the paint that stuck the best was ....... TA DAH, Rustoleum! The rest was either blistered or peeling off. Krylon was the first to bite the dust as it isn't actually fuelproof.

Can't say that any of the products were a really great finish without some sort of protective clear coat.