I understand and respect your decision on not using a non vented heater.
That being said, we have two Mr Heaters, the small Buddy and the larger unit too. We do have Propane in our coach, now only feeding the 3 burner stove. Shifted to Samsung fridge and had the old Norcold Propane feed extended to a quick disconnect to the toe panel under the fridge. We hook our Heat Buddy to this, and place it on top of the dinette table. The hose is out of trip path doing it this way. We crack the kitchen Fantastic Fan about 3", and it does have a cover over the top of it too. We open the kitchen window about 2", and I also open the front driver window about 3/4" too. I've added two additional CO detectors in the coach. One is in the bedroom area, the other is up just behind the passenger seat. And the coach has it's OEM CO detector in the galley area, above the dinette table. All three CO detectors are tested yearly, and lithium batteries replaced every three years. The OEM is also hard wired into the coach.
We use this when boon docking, in place of out Hydro Hot heating system. I also carry a 20lb tank of LP for our Webber and Amazing Campfire in a Can, so it's redundant capacity if ever needed.
We spent a week at Strawberry Flat on Muncho Lake in the Yukon on our 2014 Alaska trip. Lake was still frozen over, and we had consistent temps into the low teens, and 2 nights into the single digits. Our process was:
-Run the generator for 3 hours in the evening around 6:00-9:00PM. Hydro Hot Electric element on, and the heated Floor Tiles were on. We'd run our 1500W heater, usually on mid temp, too.
This built up a heat mass with the floor tiles, as well as the hot water tank of the Hydro Hot was at temp too. We'd close of the front of the coach when we went to bed, and usually found between my wife myself and the dog, with a few extra blankets, we'd sleep fine.
-I'm at the cycle of life when I get up two or three times during the evening:)! Around 2:00-3:00AM timeframe, I'd go ahead and go out to the front of the coach and fire up the Hydro Hot and it's furnace in both zones of out coach. For about an hour. Reading with a blanket on as the coach would heat up, as well as the wet bay would also get warmed up too. (I'm up often anyways, so no big deal.) I found that the warming up of the coach before bedtime, and then once in the middle of the night, was enough to keep things from freezing.
-I'm usually up between 5:30-6:00AM, and I'd at this time fire up the Heat Buddy. It would get the coach nice and warm, battery fan on helped air circulation. We did all find that we needed to turn on a small fan for the frond windscreen to avoid moisture build up. The DW would come out around 7:30-8:00AM to a very comfortable coach. Heat Buddy was down to low level by then, and maintaining things well.
-We'd then fire up the Hydro Hot again, to get hot water for dishes and washing up.
With the sun being out almost 20 hours at that time of year, even at lower angles, out 1200W of solar kept our bank almost always fully charged.
It was our first experience of boon docking in extreme cold temps, and we were impressed with how well the Country Coach Allure handled the cold camping. Warmed up to the mid 30's, one day low 40's, during the day. Got some great hikes in, and also would enjoy sitting by the outside fire and looking at the frozen lake for hours in the afternoon with adult beverages:)! We'd move the Heat Buddy outside with us at that time, and use the 20lb tank. Had the Heat Buddy behind our chairs, toasting the back ends if you will, and the fire on the front of us - we'd at times get too hot:)!
Really liked reading about your cold weather mod's in your Class C. And again, understand the not wanting to use the non vented heating source. For sure your decision to do so. Do you have room to add a vented heater to you mix for the future?
Best to you, and all. Stay warm - reverse of Game of Thrones here - Summer is Coming:)!
Smitty