I would HIGHLY recommend that you use an adhesive product before painting them. Plastic can obviously flex, and there are things you can use to help make sure the paint properly aheres to the plastic. My recommendation is that you use an adhesive promoter called Bulldog. I have used it on both wheels and plastic body parts to make sure the paint stays. It was recommended to me by a friend and I would recommend it to someone doing similar things. You don't have to use a product like this, but I would encourage you to do so. Just my $.02 though. If you'd like more info, just PM me and I'll give you any other details/suggestions I can.