Nah, the best solution is to put an aquarium thermometer sensor in the jacket around the water heater, stick it on the wall, and set the alarm for the perfect temperature for a shower. For me that temp is 93 in my class C and 103 in the RT. More pipe between the heater and shower head in the RT.
When the alarm goes off, turn off the water heater, and turn on the hot water faucet. Saves a lot of water and propane. The meter we use is an AQ 150. Hope the link works.