I use tung oil on mine. I had initially coated it with epoxy, thinking that would be great to keep the water out. I lightly scuffed the epoxy with sandpaper to remove the shine and improve my grip.

However, what ended up happening was that I would get little dings in the paddle, which would apparently crack the epoxy in that little tiny spot, and then water would get in and underneath. This was visible as a small dark spot around the ding. I was concerned that these spots would not dry out, and the wood would rot or at least permanently discolor, so I sanded off the epoxy and went with tung oil. I've been happy with that.

-- Dave