Air coming in cab area of class c when parked

Just a guess, but check the seal on the Doghouse.

Don’t forget that there is no door that shuts in the dash HVAC circuit when you shut off the engine. If there is an opening somewhere else that favours the prevailing wind, a roof vent, the exhaust fan over the cooktop, the fridge vent, you will absolutely feel a cold breeze coming in through the vents or floor outlets.

Try either moving the position to defrost and see if the draft changes, or setting it to recirculate, and see if it stops entirely.

JaxDad wrote:
....or setting it to recirculate, and see if it stops entirely.

That would be my first advise.

With the engine running, set your heater control to "recirculate" to close off fresh air from the outside.

But I like to leave it open to allow air inside when running an exhaust fan in the house.

We drape a comforter across the two front seats and seal up around them with it to provide a cold air barrier.

On my Chevy Kodiak (cab is Express van with wide fenders) there were vents in driver and passenger doors. When I put new speakers and sound deadening in I closed off the vents. Made a big difference in how much air came inside cab area. There are enough leaks elsewhere in motorhome to make up for the loss of this air flow.
Before shutting engine off at a campsite would turn vent selector switch to recirculate as others have stated.

Thanks to all for the quick response. I will try what y'all suggested. Thanks again for the help