I can't say I have ever seen a doujin of any kind where characters have sex in a snowhut/igloo. I can't say I'm not ok with this. Although, cold does a really good job of numbing your nerves, and would probably make it hard to get off if one stayed exposed for more than a few minutes.
That's what the kotatsu is for! Also body warmth. The entire point of a snow hut is it insulates you from the outside air and keeps the people inside nice and toasty.
Yes but with the kotatsu and everything wouldn't the snow/ice start smelting way too fast? I'm not an igloo/icehut expert but I mean, it didn't look that strong of a build. They didn't use separate blocks as it is usually done, which makes it weaker from the start, and tbh it was tiny as f.ck. it's like they minimized when they entered the hut. But as is fiction so i'm gonna stop applying logic haha
If it's cold enough outside (and evidently it is, since it's still snowing) then heat will conduct away from the interior of the walls fast enough that the snow doesn't have a chance to melt. The inuit would warm the inside of their igloo with fires. This is a little less robust than an igloo, but It's plausible it could hold up for awhile, at least until the weight of the extra snow collapses it or the weather changes enough to melt it.
Actually, the biggest problem they've got here is putting themselves in a confined space without any ventilation. (they didn't cut any ventilation holes, and they blocked the entrance with a door) It'd start feeling stuffy pretty quick, and if they're not careful they could get carbon dioxide poisoning (That said it shouldn't be too hard for them to dig their way out if they start feeling weird)