I use two strips of 12" Flexwatt hooked up to a Herpstat 4 ( http://www.spyderrobotics.com/index....products_id=36 ) which is working extremely well for me.

Before I upgraded all of my racks to Herpstats I was using a Ranco ETC Thermostats ( https://www.amazon.com/RANCO-ETC-111...ature+controls ). It goes for $40-50 on Amazon and always worked well for me while keeping a tight temp range in my tubs/cages.