[Dekatron]

The simplest designs for this that I've seen is when people make simple molds from clay, used for pottery making. If you make one top and one bottom piece with a shaft in the center you can both cure and preheat them in your home oven and then preheat the perspex with a hairdryer and press it between these mold pieces.

There are other materials you can use for the molds that will have a more shiny surface so the perspex will look nicer, no scratches and marks after pressing, or you can cut out pieces of baking paper and put on to of the mold to protect the perspex surfaces. Some people use silicone spray or silicone baking papers.