Two part catalyzed urethane, period. The best product you can afford ($200 gallon or so) When was the last time the paint on your car peeled off? It doesn't and it sits out in the sun day after day with very little care applied to it. Traditional varnish dates back to the 1500's and it hasn't changed much. Automotive urethane has had multimillions of dollars spent on research to develop these products. They are incredibly uv resistant, film thickness is very tolerant...thick or thinly applied, just get the ultimate mil thickness right. They buff out, repair incredibly easily and last a phenomenal length of time. Maybe we should start using one part paints on our hulls and topsides! Guess what, no one would dream of opening a gallon of oil base paint and start painting their hull so why would you do that to all the bright work. There's a myth that there is something magical about bright work finishing. No such thing. Put the most advanced product on it and don't touch it again for years. Other than that I have no strong opinions on the subject!