The cooler in the photo is not mine. I have a piece of flexwatt that's 20 inches long - back wall only.
I put the probe in an empty 6qt tub and it did reach 89. The tape is not full on all of the time but it does turn on frequently (blinking red light).
I ordered a bigger fan. I have to figure out where to mount it to get the heat to circulate properly. The bottom shelf is cooler that the upper two.