I don't think you do. This battery gauge is USELESS if it doesn't monitor both the in going and out going current at the battery. If you only measure the charge controller's input to the system and don't measure the draw of the RV an inverter then the gauge will always say your battery is full. It does not calculate "battery level" based on the voltage. It calculates it based on the size of the battery bank, the current in and out, and the length of time the current goes in or out.
It must be installed with one terminal connected to the battery negative and nothing else. The other terminal gets connected to every other negative: inverter, charge controller, and 12v loads.
