Thought this might be interesting, since I basically am doing this by following the other blogs, and the instructions/plans don't tell you how to.  The slot for the keel is made by wrapping some plastic around your keel, then glassing over that to form a keel-shaped tube that will become the keel slot in the bottom of your boat.

Here you see the sleeve made of 6 layers of bi-axial fiberglass cloth, with 1 x 3 wood blocks being epoxied around the keel.  The wood blocks will give me something more solid than just the glass.  I used some high-tech clamps made of rope and sticks to hold it all together while it cured.

In the end, it doesn't matter what kind of clamp you use, so long as you can get it off the keel and it slides nicely.

In my case I might have made a mistake by forming this before doing the final painting of the keel.  I think it was Kevin who had problems because he skipped ahead like that also.

In any case, I'm happy with the fit at this point, and if anything has to be sanded, it'll be the keel.  Now to get this thing properly aligned and epoxied in........