How do I contain heat in tubs?

[snakesRkewl]

As said, as long as you maintain 75 and above you will have no issues.
With 11x12 inch flexwatt under 41qt tubs I maintain about 77 degrees on the cool end with an ambient room temperature of 73.
Ball pythons do not need it warmer than that on the cool end

I do not put holes in the back of any of my tubs, this helps maintain the higher temps on the warm end.