[DutchmenSport]

The cold draft coming through return vent under the steps is caused because air is blowing inside the underbelly. The chloroplast needs to be sealed. This is where the air is blowing in under the floor and thus, blowing in the return vent in the steps.

The return vent in my camper is not ducked at all. It's designed to pull air from the inside of the living area and also pull the air from the inside of underbelly, as the underbelly is heated also, and the furnace return pulls from all directions. It's not vented anywhere. It all open.

The return on your furnace will circulate what the furnace actually blows out. And when the furnace is running, this works well.

However, when the furnace is not running, any air leaks from the outside of the camper will blow through that same space, and across the floor of the lower living area.

The best way to stop the drafts is to seal up the chloroplast underbelly with a BUNCH of caulking and/or sealers. Close up any holes with expanding foam "Stuff" too. Close off all the holes, leaks and openings where the chlorplast is connected to the various frames, it's joints, and open, cut locations, and that WILL stop the drafts from coming through the furnace return vent under the steps.

I was (somewhat) scolded on a different forum when I stated this and the conversation led to the camper needing those drafts to run the ceiling fan vents. Poppy-cock!

If the underbelly is sealed tight, and you need to run the ceiling vent fans, crack a window. That will let the air flow and suck out any moisture and keep your camper warmer as all that air is not being pulled from under the camper, across the floor, and out the roof vent fan.

Furnaces returns will pull only the same amount they blow out. Gaps in the underbelly allow the furnace to pull cold air in, and also keep the air being blown into the living space to be not as warm.