Jerry,
Great detailed photo. That was great foresight or is it insight, to isolate the potable water tank from making contact with the hull. Here's an off question for you. Have you ever used an oxygen displacer (like argon) to inject into the can of your favorite paint or varnish finishes before placing the lid back on? I just order a small pressurized can of argon to do just that. Don't know if it will help, but I hate getting that skimmed over hard layer from half empty cans of spar varnish.