I've remembered that I did make some in Perspex. But I only use the cardboard ones as they can be thrown in back of car. They're covered in gaffatape! There's a flap of Gaffa at the bottom and Velcro up one side. A thin strip of velcro on the windscreen pillar locates it and the flap of gaff is trapped by the door when closed. They don't get blown off at speed. Also, they can stay on under the sidescreensif needed. In honesty I hardly ever use them but they do work. If they were nicely made.......
