By far the worst rust I have on the rails is on the diagonal rounds. The rest is more surface rust. I certainly want to avoid removing the outside 1x6 as that requires removing my custom fencing completely (Ben has a picture of my pool here somewhere). The 4x4's seem in good shape, and, since it is an "Add-a-Deck" they don't have the extended cantilever to support more than the 2' wide deck. Where we extended the deck a few years ago (on the East end) it is self-supporting, not relying on the FantaSea structure.

Looking at the price of A-C marine-grade PT, I have to say it's far, FAR cheaper than Leisure Living's wood walls--about 1/4 the price. Using wall foam over the ply means that you CAN use duct tape (not recommended when the liner is directly against the water wall. So I'm seriously considering taking your advice on that step. Even at $40/sheet, 14 sheets of marine ply are STILL, at $560 far less than the $$1800 + shipping quoted. That's a great idea!