I had pretty good luck with Fusion on KDX plastic. Granted, I painted white-over-white (side panels), but as long as I kept fuel and Brakleen off of 'em the paint held up pretty good. I cleaned the side panels with hot soapy water, then some lacquer thinner as I recall (do a spot check if you try it) and another round of soap and water.
Any time you contrast colors (paint black over white) you're sure to notice any paint weakness (chipping, scratching etc) much more easily.
re: 'bodged paint'
That's not good, right?
Just kidding. I remember the Aussie primer awhile back. Like...you can't tell what that means by its useage? ;)