To help prevent moisture build up when storing, you could try putting a bucket of No Damp or similar dehumidifier in the storage container/garage/shed area right by the boat. We've recommended this to outfitters who store their entire fleet in a sea train or similar storage area.
No matter what, especially in confined spaces that aren't climate controlled, you will have moisture. You could always give the boat a once over midway through winter just so it doesn't have a consistent build up for months at a time. As a similarity, safe manufacturers recommend opening up your safe every few months to help prevent moisture buildup.
Also, make sure not to store directly on concrete, as this will definitely create/trap moisture.