Fairing
I did the Rustlok thing on my iron keel and was not impressed when rust appeared in a season or two. A better method is to coat the keel with epoxy within an hour after sand blasting. Grinding, sanding and painting is a waste of time. I faired the keel with VC watertite. I spent a lot of time on it and it looked great at first, I found this type of epoxy filler to be very brittle and it cracked. Since your keel is going to rust again I'd fill the joint with 3M 5200. The 5200 is strong and will actually flex a little where the epoxy ould crack