Very limited experience, in the 1960s and '70s using back-packing kit on
Dartmoor. We avoided freezing conditions though!
We certainly found fly-sheets well worth having, so a double-skinned or
inner and outer arrangement would seem to be better. The heat
insulation and better weather proofing are important, and condensation
inside is less of a problem if the inner surface can be kept warm.
Condensation is probably the biggest problem.
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-- Whiskers
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