Check down behind the rear bumper. There are ports that let the air pressure out when you close the doors to keep from damaging your eardrums from the pressure increase. You should be also to just modify them or remove to get more air flow into the van without cutting holes. They are behind the two black vents on both sides of the rear doors.
Stephen
Recon Campers
USA first NV200 Pop Top Camper Conversions
facebook: Recon Campers
Stephen
Recon Campers
USA first NV200 Pop Top Camper Conversions
facebook: Recon Campers