Soft scrub and a tooth brush works great! As little water as possible and for as long as it takes. If its really bad you'll end up with about 90% of it gone. Sometimes its just embedded in the vinyl though, but it will help if not completely remove the stain.
-Todd and Sherri
-2006 F250 Super Duty King ranch Diesel
-2012 Windjammer 3008w
-Equilzer 1200lb hitch