I agree with the water getting in via the rub-rail. Open the boxes when the boat is outside in the sun before putting it up for storage. If the boat is stored in a storage unit, what is the humidity in the unit? If the air is full of water, the boat may not dry out quickly enough, even with fans.
2015 Skeeter FX 21
...and down goes PhotoBucket with the new Terms of Service... I predict they will be out of business or begging for forgiveness inside a month. 6/30/2017