I made a plywood wooden box, 16" x 12" x 3" (you can make any size you want), drilled holes on top surface 1/2" apart. cut a hole in side wall with holesaw, same size as my vacuum cleaner hose. Made a 1 +1/2" pine frame, (like a picture frame), same size as top surface of box, staple .040 (or what you prefer), styrene sheet to frame, put it in a conventional oven at 350-400 degrees, keep an eye on it, when it starts to soften and sag , put it over the box, and turn on your vacuum. Would suggest raising the item you are vacuforming up from the box surface slightly to help prevent webs in the styrene. Some people rest the box on the oven door to keep the mold warm, (styrene can cool quickly), but this can stress the oven door hinges. Good luck!