Last January, when I went winter camping the Adirondack Mountains, I tossed 2 body warmer packs inside a homemade cloth case into the foot of my sleeping bag about 45 minutes before I got in the bag. The bag was very nice and warm, almost too warm.
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Our most important survival tool is our brain, and for many, that tool is way underused! SBRaider
Head Cat Herder