Using a window unit A/C to pipe cool air into Camper Shell

I don't see why your idea would not work. I would use some type of duct, like a clothes dryer exhaust or something flexible, to vent the cold air from the A/C to the truck shell. It would be a lot more efficient than just setting the A/C in front of the window. You could also install a small fan (computer type) in the duct to increase the airflow.

Make sure the generator is not close to the A/C, no point taking a chance of sucking in the exhaust.

Keep us updated on your progress.