I had this problem. I made my saddle according to the measurements Ron gave me.

2 @ 11 ¾" (298mm)
2 @ 13 ¾" (349mm)
2 @15 ¼" (387mm)
1 @ 15 ¾" (400mm)

It's fine for me. I bought the rubber at a sailing shop.

Tomek

email (option): Tomasz-laciak@wp.pl