i took some fine grit wet/dry automotive sandpaper to the fender wells just to give it a tooth. cleaned it up good and then used frame paint to seal the deal. frame paint doesn't require priming, goes on easy and is easy to touch up. :yup:
Another option is Undecoating which is used for automotive wheel wells. I grabbed a can for a few bucks at the auto store and its didn't need sanding just clean dry surface. It's rubberized and easy so spray clean.