when overing a summer in az. I installed the largest window a/c unit I could find. to help my rooftop unit. the place still got hot.. I found that by using another window, I could just use a swamp cooler while I was gone and at night. then seal up the cooler during the heat of the day and just use the ac units... wasn't a pleasant summer..
if/when I replace my old rv. I will be downsizing. but will have twin a/c units and add an extra 1-2" of insulation installed in or on the roof. even if I have to have it done by a non dealer source.