Larry Peterson used vinyl plastic sheet from the home improvement store, utility knife, scissors and lots of zip ties and a couple pieces of velcro to put make these inside Fenders.  The vinyl used was something similar to this: http://www.lowes.com/pd/Parkland-Plastics-Plas-Tex-48-in-x-8-ft-Embossed-Matte-Plastic-Wainscoting-Wall-Panel/3436816