Welcome.What you'll need to do is wash the plastic really good with soap and water.The paint suppliers also make alcohol based cleaners for plastic.Then sand it with something fine like 800 wet or so-plastic exagerates scratches compares to sanding paint.Another option is a wet grey 3M scuffpad.Spray a coat of plastic adhesion promoter on it and then paint as usual.I like to destatic the plastic.PPG's 103 plastic prep (cleaner) doubles as an antistatic agent.Mist a coat over the surface before and after you tack it off.Works great and the job will come out much cleaner.
