Yeah, you're going to need a really good spray primer. I'd recommend Rustoleum Plastic Primer, or any other primer intended to be used on plastics. Roughing up the surface a little bit with some fine grit sandpaper is always a good idea. After you've added your primer and your spray paint, you can also add a clear coat to seal the whole thing and protect it from getting chipped. For example, something like Krylon Crystal Clear.