I once mounted a standard window AC unit from Sears in the bottom of a popup, To be honest, I don't suggeste doing this as they are not all that effective, sun load on a tent is rather great
I used the same AC unit (The very same AC unit) in my bedroom at home. And later on a Scamp (replaced a window, did a bit of framing to seal it in properly) On the scamp, which is a firberglass bubble, it worked rather well. For years I never saw another scamp... Then we towed it up to General RV and towed the tow vehcile back home with a Class A, Since then I can't hardly climb into the driver's seat of the "A" w/o seeing at least one SCAMP on the road.