Working on planning line routes. The tanks do nest nicely. I measured them at 33.25" when perpendicular. Not a problem because there's plenty of extra foot material that I can cut off to get them down to 32.5" I was thinking that the posts were splayed a bit, but they are parallel to the tank sides. There will be 1.5" of headroom above the tanks and in between the 1.5" tubes to work in and none of the ball lock couplers land directly underneath any of the tubes.
I've been wracking my brain over the lines and fittings. Have to wait for the air tanks to get here before I can figure anything out for sure. I want the lines to enter bottom tank ports so that if water does ever reach the expansion tanks, it can drain right back out. A ball float check valve would be handy, not particularly necessary, though I would be wise to T the air lines to a single port for check valve installation. I don't think changes in temperature or elevation will really be of any bother - especially with 10 gallons of expansion, thus I'm going without valve for now.
Water lines, on the other hand, need to manifold in parallel to something closer to 5/8"/-10 or 3/4"/-12 before branching off to the 3/8" PE-RT(newer PEX) home runs. I've been browsing various AN fitting and weld-on bung options to make some kind of manifold run. Might have to see what I can come up with for a PEX tube turned into manifold with T fittings. There's not a whole lot of room where the liquid fittings reside.
The plastic ball locks may be fine, though I am going to both fill a tank with water and hook up my compressor to an unconnected and connected fitting and run it to 100 psi to be sure that the fittings won't blow apart as soon as I open the gates to the installed system. Don't know until I try because the kegging articles I pulled up never mentioned anything above 20 psi.
Expanding on the SketchUp model of the tanks in the pit, I added the rusty walls/beams I have to work within along with the 1.5" cross tubes. I'm starting on the wheels tubs next so that I can figure in weight with functionality.