We live in Northern Wisconsin with our 2015 Bounder 35K. Thankfully, we have not experience you difficulty's with the dead batteries.
Just above the entrance door in our coach, there are two switches that will kill the electrical juice in the house and the engine. When ever we leave the coach, when it is not plugged in to shore power, we will put those switches in the off position. Even if that would be for a few hours.
We also disconnect the inverter power, when leaving the coach for a few days. Right now, we have the coach in winter storage. I pay a visit to the coach on, or about, the first of every month that it is in storage. At that time, I start the engine and also run the generator for at least a 1/2 hour. I run the generator with a load. When i opened the door today to make my inspection, I first checked the main and house battery status. Both were at full charge. I still ran the engine and generator.
When I left, I turned off the inverter and the two battery disconnect switches. I have to remember to extend the steps before turning off those switches.
Jim