Furnace wont keep trailer warm
Had the same type of problem on my Rockwood 2701SS. Like others have suggested, check your duct work where it attaches to the plenum. Mine was not attached, just sitting there in front of it,thus I had very low airflow. I have used my trailer in much colder temps than 40 F, while moose hunting, and the furnace has no problem heating the Rockwood since I attached the ductwork at the furnace.. As others have suggested, check the main duct connection first.