Of course it will get scuffed up and doused regularly, and sun will work against it. I don't use epoxy under it, I don't think it adds anything to the life span but may add work to re-newing the varnish. What's the sense?

The more coats of varnish you put on, the longer it will last. With the wood sitting on horses in a warm place, a long winter, go at least 10 coats. Don't quit until you can shave in the reflection.

He wants a bright floor in his dinghy and he sounds like a nice guy, give it to him.