I've heard Krylon Fusion works well. It supposedly fuses itself to plastic. As for prep work, all I would do is wipe it down with denatured alcohol to get rid of any oils on the surface. But the inside of my hard top is already rough I can't see a reason for sanding. Someone else can better guide you in this area though.
Use Locktite, Or Kiss Your Nuts Goodbye!
Small like a CJ, better than a TJ!
☼ YJ ○⌐ EVER ☼