I have a couple of portable A/C units at my work. I guess the more expensive ones are quiet, while the cheap one is kinda noisy.
Make sure that is has two hoses, so it will take in outside air to cool the compressor. The single hose units take air that is cool and de-humidified from your room and blow it outside, sometimes so quickly that is it hardly worth running it, because so much unfiltered and humid air will be coming in anyplace it can to make up for the 100 CFM exhausted air out the window!
9,000 Btu is about the largest that the generator can support in addition to the rooftop unit you already have. Most of the window adapters are set up for square end windows. The plastic is probably easy to cut with heavy duty scissors or perhaps some sheet metal sheers.
You might also try taking in air from the window, and blow out the hot air through the roof vent in the bedroom. But you can not take in air and blow out from the same roof top vent, they are to close together.
Good luck!
Fred.
