We've been messing with perimeter stringers and high density rails. I refrain from calling them arabolic stringers because I can't see any parabola in there!
I believe that there is some significance to having molded high density rails, but I am at a loss to explain why. When the rails are high density but not molded to the final shape the pop and drive of the board is less than when the rails are molded to the final shape. I know that to many purist - molded or popout is a bad word, but there are some decided performance advantages, I believe, when bits and pieces are used.
James from the TWC - the green along the rails marks the stringers.
Molded rail - the bottom rocker and the inside stringer location perspectives. Still needs some of the flashing cleaned up.