If you have no bodywork to do then I would just scuff it with some red scotchbrite then start the painting process. Some say no scuff and some say scuff but my opinion is 2 hrs of scuffing is a small price to pay to make sure the paint adheres and lasts. I also think you should stick with one product line as Krehbay suggested. As always everyone has their own opinions and these are just mine.
