I bought 10m of 135gsm fibreglass, and laid it in two strips either side of the centreboard case, with a little overlap where the keelson will end up. Here's the first side placed. It was quite a bit easier than I anticipated. Just lay the fibreglass on the hull and pour some unthickened epoxy on top, then work the epoxy in using a plastic squeegee. The fibreglass just lays down nicely. Then once the epoxy has had a little time to set up, the excess gets trimmed. The photo shows in between trimming the edge and the stern.