I use a different system to mount & seal sponson tubes that doesn't require any screws, clamps or blocks glued inside the hulls bottom. A solid 3/8" OD carbon fiber rod passes through & is a snug fit in the 4 machined aluminum sleeves which are epoxied in reinforced G-10 areas. The 4 machined sleeves have a machined groove inside for the tight fitting silicone rubber "O" rings. The 2 solid 3/8" OD carbon fiber rods are held in place with short carbon fiber telescoping tubes epoxied on the outside of the 4 machined sleeves. The solid 3/8" OD rods extend into the telescoping tubes epoxied into the sponsons. The sponson telescoping tubes are glued into place with a jig to ensure precise alignment. 3M, "90 degree" nylon reinforced tape securely fastens the short carbon telescoping tubes to the telescoping tubes epoxied into the sponsons.
Jim Allen