I'm trekking up the Kilimanjaro and planned on using my sleeping bag which is rated for -10 / +10 with an extreme at -17 degree Celsius. I read that temperatures may plunge down to -25° at the very top, although I don't know how cold nights at the camps are to be.
I was planning on making my own Vapor Barrier Liner in case I get cold, despite the bag and my cotton liner.
My plan is to use a heavy-duty garbage bag (to prevent moisture from leaving), add infrared radiation reflection with a thermal blanket inside of that, and to make things cozy, slip in my cotton liner.
Is this a decent homemade vapor barrier liner? If not, how can it be improved? Also, how damp may my cotton liner be in the morning with such a system?