Is this for ball pythons? ... cool basement or not, an 8 - 10 degree temp gradient would be pretty hard to achieve with 11" heat tape under a 27 qt tub.

If your basement is that cool, you might want to consider 3" heat tape under the rear 1/3 of the tub AND 3" heat tape under the front 1/3 of the tub with either 2 thermostats or a thermostat and rheostat used in tandom on the two heating "zones".

-adam