First of all most Class C's have the house-batteries used to start the generator.
How cold was it when you tried to start the generator? What do you have for house-batteries? Where the batteries left stored on "disconnect"? How long since last full charge?
Any time the temperature is below freezing the MH engine should be started first and let idle for at least 10 minutes. The alternator should be charging the H-battery(s) with "disconnect" on or off. I normally use the H-battery switch now to energize the solenoid (or solid-state) to connect the batteries.
You should hear the solenoid click to make the connection. They can stick in cold weather and need cycling of the switch a few times. The reason for starting the engine first is that the alternator will raise the voltage sent to H-batteries from 12.6 volts or less (actual bat. voltage) to 14.4 + volts.
The extra voltage is needed to start the generator in cold weather. The generator should be tried to start with the MH engine idling. When the generator is up and running for at least 5 minutes the MH engine could be shut down.
I suspect you new motor-home may have a bad connection or ground somewhere in the starting or charging 12v circuit.
Also; why would you need new batteries 7 months ago on a new 2013 Class C MH? There has to be a problem in the 12 volt circuits that was not addressed by throwing new parts at it.
