Any single pack alkyd will do. I got mine fresh from the factory at HMG in Manchester, I used the coach enamel last year but its pricey so years before that I ordered the Speedline coating, not quite as mirror shiny but I also paint plant equipment with it no problem, so it's more than tough enough for the rigors of a canal. They make the coatings for a few brands including one that sells it exclusively as paint for narrowboats. If you give them a call they will give lots of good advice on choosing a top coat. It's important to check that your top coat will not react with the undercoat so eit