I'm getting ready to coat the underside of my MK4 body with U-Pol Raptor bedliner. I've scuffed the fiberglass with 120 grit, and I'll clean it all good with acetone. Is that sufficient? The U-Pol website seems to indicate it is. They only mention the "adhesion promoter" for hard to sand places. Have any of you found the adhesion promoter is necessary?