Ditto. OSB has no edge compression strength. It will just flex, and the deck will come toppling down. Your structure needs to have some 2 by material, leading down to the hull. 2 by 4s also have more of their strength, if turned 90 degrees from how you have them. Not that you need it, as having them, over 2 by 2s is just extra weight, as it is, but still. How do you think you seats are strength wise? Is there enough beef in them, to support the deck by themselves? IE, have your structure attach only to the seats, and not need any downbars. Now, you would need your structure to span all the way across the seat, so the load is supported by the whole seat, and not the edge.
