Welcome to my world! I am in the high country. its 35 at night in the summer. Its your battery voltage. I called my Dealer and said I have a brand new TT rockwood mini and the furnace is broke. After years of trouble shooting i found it is the battery. Even if my batteries are 2/3 full on the indicator it wont sustain. I have had to plug in the hitch to my truck to run it. So with that, get bigger batteries
Best of luck