The generator will need good airflow or it will overheat and cut off.
There were several Class As and Cs a couple of years ago that had that problem.
Most accessory places either have or can order and extension pipe that will
go up and over your roof. They are advertised for Motor Homes and are removable for transport.
Having your generator's exhaust pipe extended outside the body-shell and attaching one of these takes the exhaust way away.
A web search show several companies selling longer exhaust pipes of various lengths and diameters.