I'm going to bet the size RHP he suggested for the size enclosure you are using will allow you to do away with both under tank heaters. The way I have my thermostat probe mounted for RHPs is drilled through the back and hanging several inches below the surface of the heat panel. Then I have the thermostat set to 86, and it provides a hot spot of 89-90. you will of course want to tinker a bit with your personal setup to get it dialed in how you want it.