Well, interestingly, all three things are required for it to function, and one of them is sort of annoying as it reduces realism in other ways, but also has the happy side effect of balancing fuel use from both wings at once. The RESOURCE string must obviously be added to the wings for the fuel itself, under standard part parameters at the bottom add fuelCrossFeed = True, and in Squad's resource folder (here's the annoying one), Change under LiquidFuel, flowmode = ALL_VESSEL flowmode = ALL_VESSEL is the same thing that governs electric charge and intake air. It evenly distributes fuel out of all of the tanks used on the aircraft, however this could be problematic (cheaty) because it means COM doesn't change as fuel drains, out of ANYTHING, since you're changing the way the resource behaves universally. Basically it makes everything REALLY stable. Things that use LFO less so because you didn't change that. Unless if course your primary concern in spaceplanes in which case you also have to change the parameters for oxidizer. So anyway, have fun with that, and if anyone finds a better solution, let me know.