I've been shipping snails since spring so have never sent them in very cold weather. Is it ok to use disposable hand warmers as a heat pack? They are non-toxic like uniheat heat packs but heat up to 130 F whereas uniheat go up to 110 F - with insulation between the heat pack and snails would the hand warmer work or do I need to get a heat pack that's specifically designed for transporting fish? Or is it better to go without a heat pack and just insulate the box well - are parcels in heated sorting offices etc most of the time or are they exposed to cold outside temperatures? Thanks.