Hi Rob,
As Joules said Kapton tape is both a good electrical insulator and will conduct heat readily. If its thermal insulation you need, an air gap would be as good as any.
I used to have a similar press that I built, that I used for embossing plastics and some other materials. I used an 8" solid hotplate from an oven hob along with a washing machine thermostat to control the temperature. It worked very well. The clamp handle was made from wood, but the base was the part that suffered from the heat. Its not too long ago that I disposed of it.