Annie Hope wrote:
I could turn of the gas bottle each night.
That would be good. Motor homes have been known to go up like Roman Candles and the world needs every permie it can get!
So I'm thinking in terms of "camping". Multiple layers with an air gap in between - a tent plus a "fly" - may work as well or better than something thick and insulated which could trap moisture inside it and promote mold. Wind will be stopped by the greenhouse plastic assuming there aren't a lot of vents that close poorly (some fresh air is a good thing).
With camping, a key thing is for sleeping bags to be stuffed first thing in the morning to push all the warm, moist air out - my concern if the greenhouse is growing plants will be the humidity. Our climate is very damp all winter, and we had to move a dehumidifier into the bedroom during the day to dry out the bedding. (I don't like the noise at night.) So I'm not sure from the picture where the bed will go and whether it's possible to put plastic between the plant area and the temporary bedroom. Similarly, cooking often produces a lot of steam from both food and washing up. Will the HRV unit deal with that?
Another thing we use is called a "bed warmer". It's sort of like an electric blanket except it's designed to go between the mattress and the mattress pad. They aren't cheap, but it puts the heat exactly where you need it. In really cold weather, I turn it on for an hour before bed so that it heats the bed and blankets and that also helps to make sure things don't feel damp. We overall use much less electricity with the bed warmer than if we tried to heat the air in the room. Of course you could look for the old-fashioned equivalent which is a special metal pan with a lid that they used to put hot coals from the fire in and rub it around under the blankets before climbing in. Another advantage of the bed warmer is that if I wake up cold at 4 am, I just push the button and it warms me up again. That's often all I need to get back to sleep easily.
So I suppose what I'm saying is that your idea has potential. Using a serious camping sleeping bag, rather than regular bedding might be necessary to make this work in weather that's giving you frost. A lot depends on the individual - I don't warm up easily once chilled and need an external heat source to do so, whereas my husband generally doesn't have a problem.
Possibly, rather than looking for second hand quilts, I'd watch for wool blankets. My gut feeling is that they'd do a better job.