Anything to redirect exhaust is a help. The systems to carry exhaust above the roof are great.
Back in the days before AC was in every car in Bermuda we would ride around with hatchbacks open. Trouble is, our own exhaust would get sucked right back into the car. The solution was simple. A piece of vehicle water hose elbow to direct the exhaust to the ground or side. Same would held with a genny exhaust but direct it up. Not as good as a top discharge but much better than blasting CO at your neighbour.
Of course keeping genny run time to a minimum makes for good neighbour relations too.
