Sam2 -“Health: And what’s the Heter in places where it’s not cold?”
I never slept in the Sukkah until recently. (I did when I was in EY.) I was Soimeach on Metztayer either because of cold and/or danger. (And when I was married I had a third Heter.)
The MB says (above post) cold isn’t a Chesoron of Kein Todoroo until the last line which I try to do now (sleeping bag). Seems to be a Machlokes.
As far as danger -Sharrei Teshuva there -SK Heh -that brings an Achron who argues on this Rema. Also MB #20 brings Achronim whom say B’deieved you are Yotze eating in such a Sukkah!