Whenever we park or I empty tanks we refill all sink/shower traps. If last thing done was draining tank, the vent is not big enough and it will pull all water out of traps. I believe makeup air for furnace is inside coach.
Furnace is air to air heat exchanger and all hot side is outside coach. Also dead frog, lizard or mouse in vent/ducts can create terrible smell.
We are in central Florida and on recent trip to NC (snow) it was raining dead tree frogs from under coach. They stink pretty bad for a short time.
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