I've racked-up 7+ years of outright homelessness, & 1/3-decade of homeless-in-the-Canadian-bush:
IF you want to survive cold in a tent, THEN you require:
double-walled-tent is better than single-walled: the more walls, the more dead-air-space insulating you.
Tyvek-type-stuff works well, breathes sufficiently ( you'll be full of mould if you just use polyethylene ), & may be cheaper when bought in big rolls, for making framed multi-layer tents for families.
You want the roof to be steeper than 45-degrees, for shedding snow, or flatter, for holding it: 45-degrees is the it-can't-make-up-its-mind angle, & be aware that ice sticks to tent-materials, so snow BUILDS on tents, if that's happening, there.
Stick tarps over, or string fabric inside, parallel to the tent-walls, to improve the insulation ( improve, not make-perfect-for-some-arbitrary-degree-of-cold ).
Fleece is the best insulation I know-of for wearing, for long-term blankets or sleeping-bags ( doesn't waterlog, the way flannel or even wool does, when you're sleeping in it every night ), & you need about 1/2-metre for -30C sleeping if your metabolism is strong, but that same insulation will only be sufficient for about -10C if you're old & frail.
Propane for cooking is required, also for melting ice, to drink ( the smog from wood fire will drastically shorten one's life, unless one has a properly-chimneyed wood-cook-stove )
Maslow's hierarchy-of-needs: protect-the-life-1st, when everybody's life is secure, then begin working on the next-level-up of the hierarchy.
Hot-water bottles are a real boon, in deep cold, for keeping you warm longer, at night, in your sleeping-sack.
You probably want giant ( 2" ) bulldog-clips if you are using blankets, to stop them from all sneaking off-of you, once you begin sleeping: clip the edges together, to keep them on you.
May this help save someone's life in some such situation, somewhere: I survived my homeless accumulated-years, but many don't.
I want needless wasting-of-our-lives pushed-back.
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