Dont wetsand the bondo itself. Use 40,80 or 180 to get the bondo correct first. Then prime it. Then wetsand with the other finer grit papers. When I paint something I never go above 400 wet sanding before I spray it. It leaves the old paint and primer very smooth and makes a real good paint job. Once you have it painted, the use 1500 to 2000 grit to color sand the paint before you high speed buff it and wax it. Good Luck.
