I prefer my UTH's but they require a thermostat (I use and highly recommend "herpstats" by spider robotics), and you really can't have a thick layer of substrate. I switched from shredded aspen to corrugated wrap when i switched to a UTH.

here is a link if you are interested in corrugated wrap:

http://www.papermart.com/Product%20P...x?GroupID=4608