The Hammerhead 12 has 1/6 ply with 1/32 ply laminated to it. as far as the Sponson rods. Like Ron said, we are using .188 solid rod & yes they are shoved though an 7/32 OD .014 wall aluminum tube that goes through the hull & another tube that goes in the sponson. To hold them in place, some guys use electrical tape or others use 7/32 ID rod collects DuBro makes them, otherwise the collects are next to impossible to find.
Hope this helps. if you need a picture, I can email you one.