let me just start off by saying that I love my HH. with that said I do not have much experience sleeping in it during cold weather. I was thinking about ordering the undercover and underpad from HH website. I know its hard to say because there are other factors that will come into play but at what temps would the Super Shelter keep me comfortable using +20 northface sleeping bag. I know that really low temps would require a down underquilt but i am trying to not spend $300 to keep me warm at night. any help with this would be awesome.