Just a FYI
If you make a scupper style DO NOT overload your kayak or leave it on the cart for long peroids of time. The stress on the edges of the scupper can cause the hull to crack. You wont notice untill it is too late and you are sinking far away from the launch.
Google it first. Here is a vid of a really lucky (cause he is alive) guy that this happened to.
Stick with a cradle style diy or C-tug
sinking kayackOB