Our LQ is only about 18' of our trailer (counting the bunk) and the ac will freeze you out sometimes. I always have the roof vents open in there when running heat or ac, seems to work way better that way.
I also wonder about moisture in the rear, I'm thinking even with draining the actual water, it's going to get pretty moist and humid back there. I would suggest a floor level vent or two to work along with the roof vent to get some airflow through there to get both the heat and moisture out. My motorcycle trailer has one on the right upper wall and the left lower wall which allows a little airflow through the trailer and the thing isn't an oven when you open it up. I'm thinking the same thing down low on your wall would do the trick to get some airflow going up to your roof vent.
2-Piece Polypropylene Trailer Vent for 3" Diameter Hole - Black Redline Enclosed Trailer Parts HMAV2-AVT2