It's supposed to work like this:
You can see the white supports. Two coats of bilge paint. Heavy-duty hardened steel self-tapping screws.
The taped-together piece of cardboard is the pattern for the shelf that sits down there. It's much easier to build it with the supports screwed in. I didn't take a picture of the plywood piece. But. I seem to have managed to get the supports close enough to level that the plywood sits down there solidly.
What a relief.
It was a little dodgy getting the supports all reasonably aligned and more-or-less "level". It involves setting the spirit level up on the bunk to see which way we're heeled and then moving it down inside the tank to parallel the angle of heel. While holding the board in place. While worrying about the height. While squatting on the aluminum.
There are 8 supports for the sections of the top shelf. They'll go in while we watch paint dry on the bottom shelf.
Right now, there's a lot of watching paint dry. The weather is cold enough that it's one coat on Saturday and one coat on Sunday and then wait a week to install. For the little supports, I could more-or-less paint both sides by flipping them over when they were tacky. For the shelf, though, it didn't get tacky before it was time to go.
It may take another weekend just to get it painted. Then we can start putting in hoses to see if the lower bladder will work out as planned.
The plumbing up to the deck was a 7′ run of 1¼″ hose. There was a 1″ pipe nipple under the deck. The outside diameter of 1″ copper pipe is 1¼″: you can slip a hose over it and slap on a hose clamp. I prefer proper barbs, so I'll replace the nipple with a proper hose barb fitting. I've got new hose and fittings on order.
The bladders need to be washed and treated with a mild chlorine solution before use. Then we can pressure test the whole thing while we watch paint dry for the upper bladder's shelves.