I had good luck with Foss Foam when replacing the rudder on my 1983 Hunter 37 Cutter. They had the mold in stock and shipped the rudder a week later - very pleasant to deal with. I did coat the new rudder with epoxy
barrier coat before applying the initial anti-fouling. 10 years later, that rudder is still going strong. I was using a stock design that they had made before - I can't offer an opinion on their custom work.