Do yourself and your basses a favor .buy a piece of nice pine (or whatever) 1X6X however long you need to hang however many basses you have (I figured 18 between basses).
I seriously considered that. But, since the studs are aluminum, which I understand for interior walls is about the thickness of a coke can (read the earlier parts of this thread), I'm not at all convinced that using a backboard like that would be better. Then, I would have 3 hangers acting as levers on that board, attempting to pull much skinnier screws out that are only threaded into drywall and very thin metal.