A wood stock is ok. Take the time to treat it with boiled linseed oil before the season starts and you won't ever have any trouble with it swelling. Remove the butt pad and coat the end as well. If it is an old gun, put a good coat on it and let it soak in, add another coat or two for good measure. Composite stocks are hollow and can retain water for a long time if not drained after being submerged. Linseed oil is cheap and a quart will last you for years.