Because the RC-30HV is a closed bath chamber, it is necessary to put the small, monitor thermistor into the chamber's outflow stream.

One method is to put a small tee fitting in the outflow line and insert the thermistor into the open port.  Seal around the thermistor with silicone grease or sylgard.

The large, white, main feedback thermisiter is placed into the sized hole on the side of the chamber base.