i have my probes on the inside of my tank. I just tape them to the bottom of the tank and hide the cords with some plants.

gives me temps under the substrate under both of my hides. I also have a ambient temp sensor in the middle of the cage. I get 78-81 on the cool side and 98 under the substrate (92 on top)

anyway.. having the probes in the tank gives me an good idea of what is going on in the tank.