Clean, Clean, Clean and then use the adhesion promoters.
With all the plastic on newer cars we are benefiting from the technology that improves paint to plastic adhesion.
However, Paint will not stick to polypropelene forever. The interior of my Challenger is dyed/painted blue. I'm trying to convince my wife that the best protection from dinging the panels is being naked. She's thinking sweat pants and sweatshirt. OH well!