I was looking at your pictures in your members photo. wow man, the one picture with the frost all over your boat looks like some scary si-fi move. Your rub rail problem. Thats what happens when people don't over think it or just take the cheapest way, take short cuts or just think they are doing the right thing. Just staple it on and crazy glue it. "Thats it for my sarcasm". Don't use wood for backing. Its cheap, cost cutting for builders using leftovers. I Did ever thing over on my boat about 24 years ago, give or take. My boat is still as dry as a bone. And I check on every thing continually so things don't get to far gone, and in the long run keeps repairs and damage and cost to a minimum. I installed large SS fender flats with polyurethane caulking, with no wood and no problem. If you think you need some type of material behind the nuts & washers use some kind of plastic. My rub rail it works excellent for my situations. I have some very long "fenders " about 45 inches, so the rail helps them roll of the hull. If you have tied up to concrete walls or canals or rusted metal docks you might think it over "but don't over think it". The definition of a rub rail doesn't mean looks. But if you are going to build something you may as well make it look good. My two cents worth.
Food for thought :
For all the westsailers who recommend using materials that don't belong in boats or to do things the cheapest way doesn't say much for our boats. Remember all this is public domain. And for those wondering why westsails are loosing there value $ are not selling it doesn't help. The market is anther story.
Lawrence..May the wind always be in your sail.