I wired my additional fans through a thermal snap disc switch.
They automatically turn on at 90 and off at 80. I also changed out the
existing 130 degree thermal switch control to the existing fans for one that
turns on at 110 degrees. I've yet to hear the original fans turn on.
The fans I added are much, much quieter and move more air.
In addition, I also added a bypass switch that will allow me to manually
turn all my fans on or off as needed. Haven't needed it yet as our Dometic 1350SL now runs in the mid to upper 30's on the hottest days. I even
had to turn down the thermo to 4 to keep from freezing items.