My AC has never been that great either. I always blamed it on all the windows, and lack of insulation in the slide roofs. I added a portable AC in the living room, and that helped alot. On a recent trip I pulled the AC filter cover off and found that the baffle between the air return side and the cold output side had come loose and fallen down! So the AC was just pulling some of the cold air back into the input side. No wonder it wasn't cooling down the trailer very well. Decided to check all the output vents too, as around some of them the ceiling was cold, but not much air was coming out. The taping around the output vents was poorly done, as there were gaps and holes that the air was escaping from. Also the AC made a lot of noise in the living room. I figured out the rear two mounting bolts had backed off about an inch. I tightened those up, and it runs much quieter now. I haven't gotten to test out the new tape job yet, but I'm sure it should cool down much better next summer!
2010 Sabre 31RETS-6
2010 Ford F350 PSD