Installing a rootop air unit isn't that hard, I just did one on my bus a couple weeks ago... you can
LOOK HERE for additional info and pictures...
The big question is what size is the opening on those escape harches? The rooftop air is designed to fit over a 14"x14" standard RV vent opening. You will also need to have basically flat area, no flange from the hatch... The a/c unit sits right down on the roof with a square gasket that goes around the opening. The gasket is slightly larger than the opening, if I remember correctly the gasket was about 16x16... if your opening is bigger than that, you may have to make a custom gasket but it should still work. The mounting system is a simple squeeze type system, four bolts hang down into the 14x14 opening in each corner, and there are some short pieces mounted at angles that you run the bolt through and clamp it together.