Built it last week. 2x2x0.5 shielded, auto-direction 485 modules, buck converters to 5 V at each Nano. All twelve answer at 19200 with zero CRC errors over two days. I forgot the bias resistors at first and got junk on node 11 (the far end) when the bus idled, adding them fixed it. Children show up in Hermetry as bench-01 to bench-12 under the gateway.