Since you have them off, paint them. Just degrease them real well, especially since they have a lot of conditioners on them now, and spray paint them with a satin gloss black. You can spray undercoating or spray paint on the rockers if you like, it wont hurt anything. If you wish to reinstall the plastic rocker guards after you paint them, it wont matter if you sprayed the rockers, you will just cover it back up. The plastic guards are there for two reasons. One , to hide the pinch weld area because the rockers aren't very pretty. And two, they protect the rockers from getting all chipped up from rocks and then rusting. If you remove the guards and wish to keep them off, sand the rockers well with a scotch pad or 400 to 600 grit sandpaper and spray a rubberized rock guard or rubberized undercoating. This will help repel the rocks. I prefer the rubberized rock guard or even a bed liner material.