To keep the roots cool i use rather big pots, which are themselves embed into larger pots. The interspace is filled up with sphagnum. It is similar to what is called 'Slack Potting' for Drosophyllum. This helps to keep the roots cooler. I measure a difference of about 5°C on a hot day. With this setup my plants are standing in my greenhouse, where the temperatures can reach about 35°C. If it gets that hot, they are shaded. This has not yet been a problem for any of my south american plant. I also grow Heliamphora hispidula like that. The most important thing for me is to give the plants a good temperature drop at night. This is, except for maybe three to four weeks, no problem in Germany.