It currently has a 2x6 (which is too thick to fit under the rail, about 1 1/4" under rail space) and I want to redo with some sort of plywood (so i can make a solid T shaped piece for more structural soundness)? I have any experiences you have had would be great.<br /><br />If I go with Ocume(sp?) marine grade do I have to seal it with anything...it is about $84 a sheet for 3/4" - 18mm.