Sven7, the wheel skirts have 1/8"x1" aluminum bar along the bottom of the wheel well to form the shape. His tires were more offset than they appeared, hence the seperation at the bottom front. Up from that, the coroplast was screwed down using existing holes underneath a layer of weather stripping. Along the top and towards the back, there is 2 pieces of aluminum bar bent into a L-shape. These were drilled into the fender, as the coroplast is drilled down with a screw that goes threw it and the bar. It is the same setup as is on my ZX2, and it works great at all speeds
