As a Service Tech I have seen alot of van installs.
I hate working on Van Mounted Pressure Washers because there is no space for anything else.
One Hood Cleaning Customer decided to mount his in a van and he no longer has a van.
He stored his rolls of plastic, chemicals, Gasoline, Diesel, squeeges, brooms, etc. in the van.
One day his worker started up the machine before removing all of this stuff and the van caught fire.
He burned part of the roof on the resturaunt as well.
You see the vent was properly installed but, the muffler was not a part of the vent system. The fumes from the extra gasoline and the plastic near the muffler were too much.
Also the engine could not Brethe properly because there was a Rain jacket in front of the motor fan and it was pulled onto the shroud of the motor.
If you must use a Van get a Box Van with a roll up door. There is plenty of space and Ventalation.
A regular van is not Recommended by me.