It would be worth adding the EN series in there, Elliott. While not as quiet or just plain cool as the EU series, they are very good generators and are more affordable upfront. The only reason I throw that out there is because I have experience with one and am considering buying one if I can get it on the cheap.
As far as plumbing exhaust together ....don't do it !. not only will the gennie feed exhaust back through the bus's engine, causing damage ( carbon buildups etc.) but the bus will also back feed through the gennie. Keep these two systems seperate ESPECIALLY when you are only using one at a time .