You can do the football shape in many ways as your read on this board. I always do both at once on dry wood with no problems. I do the football under the large piece because any strings get trapped under the large layer and disappear when wet out. I now use a 4 oz. football under a 6oz total layer. Many builders are using all 4 oz. This summer a wave picked me up a bit right on top of a rock. I got a nice deep scratch but not into the wood.

I have never built a super light boat but I have a lot of experience being on rocks.