I treat any smooth plastic just like metal or the painted plastic front and rear bumper covers, using whatever wax or sealant I happen to be using at that time. IMO, any wax lasts longer than about any trim dressing I've used and looks just as good if not better. I've even tried it on textured trim. A few years ago I did the wiper area of my then beater Intrigue as a test. I scrubbed it well, rubbed in some 303, then came back a day later with Colli 476, wiping it off before it hazed. It stayed nice and black, beading water nearly forever.
Bill