Just wanted to add a comment about the flex of the rustoleum-

I have been using aluminum foil in my paint trays so I can easily reuse them. I havent painted the car in about a week. I pulled the aluminum foil out of my tray last night and there was still a fine layer of the red paint that had dried on it. I crumpled up the foil and then reopened it- The paint was unharmed!!!!!!!!!!! I did it quite a few times and the paint didnt peel off or crack. So I would think no problem on the plastic bumpers as everyone has said.