I haven't had the best luck with Krylon Fusion.
Some years ago I built a tag-along luggage trailer for our motorcyle and I used a brand new cartop storage box for this project.
I sprayed it black after carefully following the Krylon instructions - this was years ago, and I now forget the details, but I recall I had to wash it well to remove any traces of oil from the manufacturing process.
I think I also roughed the surface slightly to give it more tooth" to encourage adhesion.
in any event, adhesion was not at all good and the paint easily comes off.
We don't use the trailer a lot, but every time we do, there are areas I have to touch up for this reason. The trailer does stay outdoors year round so probably that doesn't help.
Could well be to do with the type of plastic used in the cartop box. I'm not sure what it is - possibly ABS.
I remember when I first bought the Krylon Fusion paint, the spray cans had the wording "Works on all types of plastic."
A year or so later, the cans then on the shelf read "Works on most kinds of plastic!" Hmmm!
I had called them about my problem without any helpful solution being offered, perhaps many others had called also!
Hope it works ok for you. Perhaps others have used it successfully for the purpose you intend.
Brian & Connie Mitchell
2005 Classic 30'
Hensley Arrow / Centramatics
2008 GMC Sierra SLT 2500HD,4x4,Crew Cab, Diesel, Leer cap.