[DutchmenSport]

I had a similar problem with my 375FL, which is the same identical layout as yours, except yours has the loft over the master bedroom and without the stairs, we have a slightly larger bathroom.

The real problem is the chloroplast underbelly. It's not sealed. Oh, there may be a few screws holding it up in place, but there are gaps big enough for a rat to get through.

When the ceiling vents are turned on, the air is sucked up through the underbelly because of those gaps and lets cold air in. It comes in through the furnace, or the return vent area under the steps going to the upper level of your camper.

The solution is much easier than you think, but also take a little time to do.

When I discovered all the gaps and holes along the edge of the chloroplast, I sealed those gaps up with old-fashioned Liquid nails. You can probably use other caulkings, but the original Liquid Nails has been time tested and proven to last almost forever in all weather and wet conditions.

It took about 10 or 12 tubes of the stuff, but I went around the entire chloroplast edges under the entire front half of the trailer. The biggest gap was where the drop down frame drops down. There must have a 1/4 inch gap or more where the chloroplast was sagging and drooping down.

I pumped a lot of Liquid Nails in those gaps. I actually did that in the Summer. We noticed immediately the air conditioner cooled better, and when running heat when weather turned cold, we did not feel the cold draft on the kitchen floor any more.

And when turning of the ceiling vents, there's no longer a draft pulling through the furnace, or the return vent. The furnace actually runs less .... a LOT less and the entire trailer feels warmer.

That's my solution.

I realized the gaps were there when I removed the wall of the pass through and had to do something in the underbelly. It was pretty dark under there and the light shone like little stars on a pitch black night. That's when I realized where all the drafts were coming from through the furnace area.

Liquid Nail is truly tough as Nails and the original will endure any weather. I once used it to affix a broken turn signal on the front of my Chevy S-10 because I was too cheap to buy another assembly. The plastic catches all broke out and the entire assembly was just dangling from the wires. I put the assembly back in place and then pumped a couple tubs of liquid nails all round that assembly. It never fell out again. I had that truck for 10 more years. The entire truck was falling apart by then, but that turn signal assembly was still rock solid when the tow truck came and hauled it away to the junk yard. They gave me $100 for the truck and they hauled it away! I literally drove it to death.

So, check it out. I almost guarantee you, there is your problem.