Back in jr. high my shop teacher built a vacuum forming machine. He made a box with a platform made of pegboard with a lever that would raise and lower it and a shop vac to provide the vacuum. The lid was a sheetmetal box with a heating element from a clothes dryer (I think) stretched out and crisscrossed on ceramic pegs. You would stick the form to the pegboard, set a sheet of plastic over it, lower the lid and turn on the heat. When the plastic got soft, you lift the lid, pull the lever that lifts the platform with the form so that the base is level with the ridges that hold the plastic sheet, then hit the vacuum and presto. I wish I had some pictures of it.