Air Conditioner Performance

I had the same struggle recently with my Thor Palazzo about the same size. My AC's are ducted and I used an infrared thermometer to measure the temps inside the ductwork. I was actually getting 25 to 30 degree temperature drop so I came to the same conclusion as you, the unit just isn't very well sealed/insulated. At least with ducted AC's I could have both units working on the kitchen/living areas and managed to keep them comfortable. I don't know what type of stove that your camper has but mine is a little bit older unit and came with a gas stove. In expectation of heat being an issue I bought a 2 burner induction cooktop for the trip and believe that cooking on it instead of the gas cooktop helped a lot. The cooktop was $180 and I found a surprisingly good set of induction cookware for another $80 so altogether $260. It really did reduce the amount of heat put into the coach and is much easier to clean up.

About the only other easy things would be to make sure that you have double layer covers on your Fantastic roof fans and to pull in a slide during the day if that doesn't cause too much discomfort.

One final thing but it would be a bit expensive. I have heard claims that the Atwood AC's have more real capacity than the other brands and are quieter. I can't vouch for that so take it with a grain of salt. I have been trying to figure out how to compare brands myself but haven't come up with a good way yet.