They'll definitely not appreciate being on a heat mat as the temperature would be much too high. Remember that larvae that live underground or deep in organic material will remain cooler than the outside environment in the wild, so even if the air temperature is 100 degrees, you can find the temperature inside moist rotten logs and substrate to be substantially cooler. If you can keep your room at room temperature, the temperature should be plenty warm. Also remember that where they are found, day time and night time temperatures are very different. Day time temperatures may remain quite warm in desert and desert-like areas while night time temperatures can drop to the forties or lower on the same day. They'll definitely experience a less pronounced shift in temperatures because whatever substrate they are in will help insulate them from the extremes, but they'll still probably handle cooler temperatures than you might expect.
