leave roof vents open during winter?

I leave vents open all the time. The first year that we had our old camper, we didn't. In between trips we would get that dank, mildew smell in our camper even though we didn't have any leaks. I put a vent cover on and cracked a jalousie window for fresh air to circulate and the camper never had that smell again.

To prevent the new camper from ever getting that smell, we leave roof vents and windows open year round. We are now parked under a carport, so I don't have to worry about water intrusion through the windows.