Alright, I think I have shuttles figured out to my satisfaction.
One of the major eureka moments was slaving the oxygen generator to oxygen level detectors - made the batteries last, like, five times longer.
But now I'm struggling with buoyancy.
I can't seem to set the ship to stay neutrally buoyant in the navigation terminal details. It always either sinks a bit or floats a bit (maybe 2-3km/h) when testing. And if I try to use autopilot to maintain position, it ends up bobbing up and down pretty severely. Like +/- 6km/h. Makes docking the shuttle almost impossible.
I tried adding more ballast pumps, to help autopilot react better to inertia (or so was the idea), but it doesn't seem to have helped.
Right now I'm just fiddling with the neutral level, adjusting it to the fourth significant number, but can't get it right still. Is there an easier way?
BTW, the thing that calculates neutral buoyancy when you select the entire sub in the editor gives me some absurd values (like 0.07 for neutral, where I'm almost there around 0.4). Maybe I'm not reading/using it right?
BTW2, the sub editor is absurdly addictive. At first I just wanted to adjust some things to ease the tedium of running a boat in single player, and by now I've been overengineering the wiring systems on the shuttle alone for longer than I had played the actual game.