The bottom of that floor storage is basically in the bilge. My thought is that if the boat is sitting in the water, it might not have enough of an angle to drain out, meaning it fills with water from the bilge. Poor design yes, but that's all I can think of given that there's nothing blocking it. Can you trailer the boat out of the water and tilt up the trailer? I would try that and see if the water drains out.
take it to the dealer and have them fix it if the boat is new and only 4 months old.
Yeah, even in a new boat there is lots of debris left over from manufacturing. I've had to take apart one sailboat that had a leaky diesel tank, located under the floor. The sawdust, cut off wire ends, small pcs of wood and other junk was what caused a spot to corrode trough. Others when installing electronics removing panels behind false walls have left over caulking tubes, wood plugs from drilling holes and other junk behind there. All that stuff makes its way to the bilge for the most part and plugs up the drains. So even a new boat doesn't mean it's clean.
