It's very important to make sure you have plenty of ventilation in all areas under the seats and bunks etc. Make holes through each bulkhead and have a few removable cover plates somewhere handy to get at. Not only do these
removable cover plates allow you to use some extra space for storage but when the boat is stored for any length of time the plates can be removed to allow fresh air through the insides of all these dark places. Your boat will breath better and love you for it! ;-)