MetroMPG,
I tried to figure out the spacing of your cardboard inserts using some basic proportions. I think I have your four inserts in about the right places. I added in a fifth one where the kammback ends. The red lines and numbers indicate where the cardboard pieces are and the height of them. The green lines indicate the distance between the pieces of cardboard.
Does this look about right to you? I still need to figure out the width of each piece of cardboard, but that will be harder to do from the back view of your boattail. Hopefully you can post your actual measurements of the individual cardboard pieces when you disassemble it sometime.
Edit: Adding the green measurements together comes up with a total of 63" so my calculations are off slightly.