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One suggestion, which you will need to try by experiment - dry ice on the bottom of a Thermos. Pack some layers of insulation on top of the dry ice, and put the item on top, with a thermometer so y...
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One suggestion, which you will need to try by experiment - dry ice on the bottom of a Thermos. Pack some layers of insulation on top of the dry ice, and put the item on top, with a thermometer so y...