Diamond plate is not advised. You'd be better off cutting the plate (3/16 5086 H116) to fit, masking the edges or around stanchions with blue tape, cutting the tape edges with a razor blade to make radiuses etc, grinding (4-1/2" with an 80 grit flapper) the main field of the floor plate and painting on a non skid like Matson or equivalent. Commercial guys don't use diamond plate. For the builder, diamond only comes in small sized sheets and when you cut it to fit its a pain to get the diamonds to come out nice. you end up grinding off half diamonds etc. The other big one is that aluminum, when it gets glycol or slippery crap on it is a skating rink in extra toughs. The big one is when you slip and go down on your knees on diamond plate, you'll never use it again. Oh, 3/16 decking is normal with a 1-1/2 by 1-1/2 x 1/8 wall sq tube stiffener on 16 inch centers. Skip welded 3-9 staggered to support the plate. I know its my opinion and lots of you have diamond plate all over and love it or whatever but I've got a lot of experience with this and I wouldn't have it in my boat.