Just charge up the battery and make sure it's fully charged during the winter months. Heat is the enemy of a battery not cold. Top up any electrolytes and keep her charged up fully and you will be ok.

I stored my boat outside under a custom tarp for years and the batteries worked ok all those years.

Get an Optima Battery and they will hold a charge for over a year. They are of a special design that won't loose it's charge over time. They also charge up faster due to less internal resistance. They are spiral cell technology and worth the money.
Regards,

Moose1am