The A/C recirculates air within the coach. It takes no air from the roof. On the roof, a separate fan blows air across the coils. It's just like a residential window air conditioner.
As for exhaust fumes coming into the coach, they could enter around some slide gaskets. On our Sunseeker 3100 the slide is over the generator. I have never run a generator while sleeping. If it's hot enough to need A/C overnight we get an electric hookup site. Hopefully others will comment on their experiences.
2011 Sunseeker 3100
1997 Pathfinder Toad