The wing joiner shown on the plan is two carbon fiber tubes glued together side by side, inserted in a paper tube that goes into each wing. I did this kit for a friend, and he specified a 3/4″ carbon fiber tube to be inserted into a paper tube with an outside diameter of 13/16″.
If you like this size, you can have it that way. If you want a different (probably smaller) size, let me know and I’ll edit the little circles in my drawings. You can get carbon fiber tubes in just about any size on ebay, so just tell me what you want.
Turtle deck formers and bottom formers are cut from lite ply, just because it’s a more consistent material.