I didn't know where to post this seeing as it concerns a different car but here goes. My son hit a very large deer a few months ago and the insurance company totaled the car, we bought it back from them and I have done all the body work so far. The last things that need to be done is to paint the bumper cover and hood. I finaly have some good weather ahead of me and finished the red-neck paint both

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The bumper cover, according to the retailer, has been primered but I can not tell. Should I put more primer on it before painting? And being the cover is plastic, does the primer need to be flexible? Also if I primer it should I sand it before applying the paint?
Thanks