RE: Winter Storage - frozen
Is your board going to be stored outside and in a damp enviornment?
I If so, I'd find a way to take it to a boat dealer and after removing the vent plug completely, and putting it inside it's zipped up bag, I'd have them use the white plastic shrink wrap they put on boats and completely seal your board in a water and airtight bag of plastic.
Just make sure the board and the bag are dry before you wrap them up.
Can you not put your board up in an attic or somewhere warmer?
I've had boards go through periods of freezing temps inside storage lockers and it did not seem to hurt them in the slightest. They were in board bags (most of them anyway) and I didn't remove the vent plugs.
Has your board ever been damaged so there is a possibility of a bit of water inside?
That water, freezing inside the board between the foam and the skin, would cause a delamination for sure.
If the interior is dry, you should have no problems.
Hope this helps,