I had a 12 year old F-150 that had rust all over the water channels on the roof (terrible design by Ford), and didn't have thousands of dollars lying around to get it fixed at a body shop, so.....
After investigating a bunch of options I decided on truck bed liner (MonstaLiner roll-on stuff with their Chassis Saver as primer and rust treatment). I also used JB Weld on spots that were actually rusted through, and I painted the trim & runner boards. All that to say, lots of different surfaces and materials for paint to stick to. The company that makes the paint recommended using an adhesion promoter for the plastic parts, and said that Bulldog reacts well with their paint.
Not being particularly mechanic-ish, I read everything I could find online along with the MSDS. There's a note about polystyrene and Lexan not playing nicely with Bulldog, and some comments online about things that were ruined by using it. The problem seems to come from type of plastic, what type of cleaner or degreaser you use, and putting it on too thick.
I cleaned, scuffed, washed, and dried all my surfaces and then sprayed a light amount of Bulldog on the plastic all around. I did the whole truck and have half the can left, you only need a little. (Don't use it in a garage, you'll probably pass out from the fumes. I had it out in the driveway and still had to keep walking away to get some air, even with a respirator mask.) I put the Chassis Saver on the whole truck and then let it dry overnight. I tried to scrape it off to see how well it had stuck, and that stuff is not coming off. The Bulldog seems to have melded with the plastic and the paint.
So: good stuff, follow the directions, check the type of plastic you're painting, and be very very careful of fumes. If anyone comes near you with a lit cigarette while you're working with Bulldog, chase them away with a large stick.