> The rep
> explained that while the Captain's Varnish did have UV inhibitors in it,
> it was not designed for extended water exposure

I think the answer to your question lies in the interpretation of "extended water exposure". What is "extended"? Is it 3 hours or 3 weeks? CLC recommends Captain's varnish, unless you are going to leave the boat in the water for an extended period, in which case they recommend painting the hull.

The way I look at it, you put the boat in the water, paddle for a few hours, then take the boat out of the water. By the time you use it again, the boat dries thoroughly. So there is not a continuous exposure to water. If you were building a sailboat that you would launch in the spring, and not pull out of the water until the fall, I would say that using varnish on the hull would be a problem. But for day trips where the boat is out of the water between uses, you shouldn't have a problem.