[flyingfrizzle]

The water weight will add up big time and make the hull sit a few inches lower. Almost like having a fat chick on the boat with you at all times. lol JK
Most box stringers I see are just soaked the lower 1/3 and have filled up slowly over time. The rubber tubes in the rear are not sealed well around them and instead of draining water from the outer voids under the deck into the bilge they drain into the inside of the stringer. Most of the time I pull then out and glass over the holes. Also when they originally filled the foam in they don't reseal up the fill holes on the tops of the stringer forms. Water can get in there that way as well. Hopefully those got sealed up when they did the deck.
I wouldn't let it bother me too much as some simple drain holes at the bases will drain it out and give you some more life with out tearing the foam out if it is wet. The freezing would be the big worry if you are up north. We don't have that here so much but know it can be an issue.