Window Mount AC Install with Cargo Hatch
I had a hard time deciding which way to go for AC in this trailer. I really didn't want to deal with a roof top unit (installation or cost), and a mini-split seem like overkill for our simple camper. I do love how quiet a split is and they can be less expensive than a rooftop, but the complexity was really what kept me away. We ended up going with a 5000 BTU window AC unit and mounting it through a hatch on the side of the trailer. The hatch installed just like a window - cut hole, butyl tape the exterior frame, line the cutout with Eternabond tape, and screw in the frame. The hatch I purchased did not come with a frame, so I created one using 1/4" aluminum flat bar and framing it with wood. One advantage to this setup is we don't have to haul around the AC when it's cooler, and we can open the hatch for more daylight or fresh air. The small AC unit is easy to lift into place, anything larger and we would have had to consider installing the rear door to support the weight.
5000 BTU with 3 people in the camper on a 100 degree day is more than enough. I've been surprised how well it does on humid days too, 90+ with high humidity and the little unit will keep the trailer cool and reduce humidity in the trailer. That said, it can be on it's highest setting which we don't have to use much. We have not had any trouble running the AC with a 2k generator.