At the moment, the probe is inside the middle tub. Still somewhat trying to find the best place for it. I have since changed the shelves as well--a friend suggested more wire-like shelving since that would allow for better air circulation, so I have made that change. But I could perhaps attach the line of the probe to one of the shelves, but leave the probe itself free hanging. And I may try that as well if I continue to have issues with cool spots. Thanks for the tip!
My fan is sitting on the back "lip" where the water jug is sitting, so about even with the second tub up from the bottom. I've got it blowing up at the moment (I was hoping it would circulate air up, hit the top of the incubator, and return back toward the bottom). But since I do seem to have a cool spot at the bottom, perhaps I should try moving it to the top shelf somewhere if I can find room, and letting it blow toward the bottom. If my additional flexwatt doesn't correct that issue, then I will certainly try that. Thanks for the other tip!