It is my understanding that a frost free freezer (no ice build up inside) can have cycles where it warms slightly in areas to avoid ice crystals. If you have one it may be helpful to put your vials in some sort of container. I originally use stainless steel food thermos, but have since moved to a nylon insulated lunchbox placed in an insulated food storage bag(think grocery ice cream bag) with leftover ice bags (good old compound delivery stuff). This allows me easier access and minimum time exposed to add new and take out stored vials.
ADDING:
the lunchbox has silica packs in it and is in a zip lock freezer bag to minimize moisture. the ice blocks are on the outside of zip lock freezer bag but inside the thermos bag.
This is only because I have several years of storage, I would just toss them in there if 4-6 months.
Again the concept is to avoid temp fluctuations as every study I have seen people quote, I have not fully read any studies myself, seems to state that degradation is minimal with constant temperatures near 0 Fahrenheit for several years. Further, it seems the issue relates only to efficacy and not to any other detrimental effects. (They may lose slight potency)
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