Dean you actually only need one Acu-Rite. If you put the unit itself on the cool side at substrate level, then run the probe over and tuck it inside the warm side hide you'll get the information you need. The unit picks up the cool side temp (IN temp), the probe reads the warm side inside the hide temp (OUT temp) and also you'll see the overall humidity readout.

Take that other Acu-Rite and set it up in the room the tank is in. Folks forget that their enclosures are dealing with room temps around them so if you know the temp and humidity of the room the enclosure is in, you can help it stabilize the tank by stabilizing the room itself. In other words if it's hot there and the room is at 85 degrees already, your tank is starting at a base of that and the heat source is pushing it up from there. Make sense? Same with humidity, if it's very humid there, you need to deal with that in the room the tank is in to get the tank into the proper ranges.