So I slept in the camper last night it was a 35 degree night with no wind.
This is what I found out. The voltage read 13.6 volts at 10:15 PM as soon as I turned the furnace on it dropped to 12.1 volts with the furnace running. it hovered between 11.7 and 12 volts until the furnace shut off at 10:52 then it went up to 12.6. The furnace ran on and off during the night I woke up once at 1:39 and with the furnace on it read 11.8 volts. This morning with the furnace off and the TV on it read 11.9 volts. By afternoon with everything shut down it had rebounded to 12.5 volts.
I'm going to sleep in the camper again tonight but, I will use the oven to cook and that will help heat the camper up initially.