For small enclosures, hatchlings / yearlings i use ULTRATHERM heat mats, made in Scotland, very thin flexible under tank heaters that dont get really hot.

For larger enclosures i use heat panels & or Ultratherm heat mats, they produce enough heat to create a warm area in my vision cages.

Whatever heat source i use i always have them on thermostats, Ronco stats are very accurate & i use one on my incubator.

Ultratherm mats & Ronco stats are available at Reptilebasics.com

Hope this helps
Andy.