I grew up in Alaska.... I didn't raise chickens in Alaska but I think I really would have a heat lamp in my coop at -40* I got frostbite, it's real.
That's neat! I also grew up in Alaska, and we did raise chickens.
We only raised baby chicks in the spring & summer, so during the winters they were all adults.
When I was younger, I think they may have gotten a heat lamp in really bad weather, and I remember there was one cold snap we hauled buckets of hot water (tightly lidded) out to add a little extra heat-- they could sit next to the bucket or on top of it, at least until it cooled off again.
I know the chicken coop was below freezing inside for much of the winter, but I know it was at least a bit warmer than outside (my Dad had insulated it well, which probably helped.)
Later, we had a bigger chicken coop and Dad built it too well. With just the heat produced by the chickens themselves, at one chicken per 4 square feet of floor space, it stayed over 70 degrees inside even when the outdoor temperature was -20! Unfortunately it smelled awful because there was not enough ventilation! We didn't reach -40 every winter, just some years, so I don't remember how that coop performed in that amount of cold. I'm positive it would have stayed above freezing, at least that year (it was later modified to have more ventilation, and did not stay as warm, although it was always much warmer than outdoors.)
I just think that given my circumstances in Oregon, mommy hut is the way to go with no extra heat needed. I'm getting my littles today! Overnight temps are high 30's. I tested the mommy temp with a meat thermometer just now, it has 2 heating pads and I had to turn it down a bit, it got up to *89.
For your conditions, I do think your method sounds good.