We love our Classic 28 and there have been very few problems of any kind. We did have a dead refrigerator early on, but I blame Dometic, not Airstream. Could have happened on any brand.
I have the 13.5k BTU AC and would have ordered the 15k had I not bought at the International. That said, we have been in 108-degree temps and the 13/5 has done very well. We carry a Fantastic "Endless Breeze" 12v
fan to move cool air to where we want it. When we stop in hot weather, we turn on the AC and aim the 12v
fan toward wherever we happen to be; usually the couch. In a few minutes, the trailer is liveable.
We selcom use the furnace, but it heats extremely fast and it has ducts to the bedroom and bathroom. We usually just use the heat pump which automatically switches to furnace below freezing. It has only switched once or twice here in Texas.
I think you can get by with the 13.5k AC in GA, but if ordering from the factory, specify the 15k.
The trailer is sturdy and, I am sure, will outlive by far all of the white boxes stored near me. I had my brakes upgraded and I love the disc brakes. Few other brands have discs.