Awesome work Michael! I had planned on getting some lit up tent Milky Way photos last year but just never did. So I will just have to enjoy yours instead. Going vertical is the way to go when the MW gets to it's vertical stage.
As to sleeping bags, I don't know how the companies are allowed to keep essentially lying about how cold their sleeping bags are good for. I get into a lot of really cold temps with backpacking up to 12,000, 13,000' up. I have learned the hard way to make sure I bring along thermals, several layers, and hand warmers to be able to stay warm at night. A couple of hand warmers tossed in the sleeping bag help a lot.