RJ, Do you have your sitting in the water now on 15 barrels? IF so could you take a measurement from the water to the bottom of your outter framing?? also and see what the difference or drop is if you stand directly on the corner..? Could you feel it actually sink any when you sat in the bench's? I think i might be starting to overthink this but i really dont wanna put 2x12 if there gonna be sitting in the water everytime me and a couple of people are on there.. Im thinking i might just ad 5 more for the even 20..