Painting plastic bumpercover

I don't know if it is the same, but I painted the fiberglass bumpers of my motor home. The only way to get good adhesion was to use an etching primer. That roughed up the bumper enough for good paint adhesion but didn't scratch it up like sanding can do. I then used a spray can of automotive paint from an auto parts store. I sold the MH not too long after that so can't speak to long term color retention etc but it looked good for well over a year. Also, it was relatively inexpensive because, no matter what you use, road rocks will peck at the finish and you will have to do it again eventually and I don't want to be locked into any complicated and/or expensive processes. PS Once you have your options in your head, go to an automotive paint store or body shop and see what advice you can get from them. Ask them what they would do and how much. Then decide whether to do it yourself. (For the price of a can of etching primer and a few cans of paint, it was an easy decision for me.)