Installed the WILLHI WH1436A Temperature Controller and it works like a champ. Tested the temperature probe first for accuracy in an ice bath and it was close enough.
I really wish I had known about this device a long time ago. Evaporation has been an ongoing issue with rain gauge heaters and light rain/mist. I previously tried other devices but all had a shut-off temperature around 50f which is way too high for this area where many rain events exception summer occur below 50f.