You saw the wooden topo models in the infeed/outfeed forum. We decided that it would be fun to mold chocolates in that shape for Christmas presents. I tried the moldable silicone putty, but it was difficult to do and expensive. Vacuum formed molds seemed to be the answer. I made this very simple 6x6 vacuum former -
powered by my shop vac.
The only thin plastic around (it's Sunday and it's 2.5 hours to the nearest plastics supplier) was an empty plastic water jug from the distilled water for the batteries. It's 15mil HDPE. Very easy to melt - I used a heat gun. Here's the result. Exceeded my expectations on the first try.