I’ve got a 13′ fiberglass camper with an 8×8 roof vent with no fan. Rather than fitting in an exhaust fan, I was thinking of using a portable AC unit to duct cold air through the roof vent, and use an old furnace vent as the return. Do I even need a ventilation fan if I’m running AC? During winter, can I plug up the hole with insulation and run an electric space heater without a vent? Thanks!