Research on Waterproofing Wooden Furniture

I'm working on a pair of knock-down benches on a design by my friend Sean. These are being built with the ash I purchased last fall. I've finished gluing up the tops in one big panel that will be ripped down for two bench tops and one or two stretchers (as yet to be determined) Once the cutting gets under way, these should come together in under a day.

Since the benches are intended as camping equipment, and last year's two-week camping trip included 6 consecutive days of rain, I need to waterproof these appropriately. Some quick research turned up a couple sources.

First, from the U.S. Government, I found a short piece on finishing wood for outdoor use. This one sticks with traditional Big Box finishes—paints, stains, and varnishes—rating them on appropriate use. This gave me some thought: did I want to paint the benches, as this article suggested. Not really. And Ash wasn't on the list of recommended outdoor woods. Hmm.

So I started thinking about wooden boats, and my trip to Mystic Seaport last year. What would a boat builder do? Assuming that a boat builder would use ash in the first place. I turned up two more sites of interest: one about spar varnish and the other about a homemade polymer coating. As intriguing as the homemade option is, I think I'm planning to track down some spar varnish. I found three brands that seemed promising: Sutherland Welles, Man O'War, and Z Spar. I think one of these will end up on the benches.

If anyone has suggestions or cautions on finishing these benches correctly, please chime in.