Please let us know how that Thermostat works over time, it seems like a good idea to be so compact and so cheap. I always recommend Ranco Thermostats since they are the cheapest, yet very good quality and they are used in everything from brewing beer, to regulating heat pads.

If your Ambient air temps are 87-90, the floor could be a lot higher than that, i would stick the temp probe in between the actual heat pad and the tank just to see how hot it gets down there. If its anywhere over 115, i would worry.

Personally i keep my racks set at 101 degrees, the inside FLOOR of the tubs are 93.5 and vary by about 1 degree, the front of the tubs are room temp which is always 78-81. This is why i always recommend a Infrared Temperature gun to check the floor temps, cause thats what matters the most.