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one of the things you could potentially look at is the silver foil-lined underlay they use with floating floors as a sound dampener/moisture barrier. it has foil as well as a thin layer of foam. easy...

got one of these on the way, will give it a run and see. I'm guessing the join in the middle is less insulated than the V's so the cold creeps in. might be ok on the diagonal. the singles I have are...