I have a solution for this which may be worthy of consideration, it works for me, but YYMV.

add blocks of foam to the tanks using snoopy loops, which are ditchable in emergency. Compressable foam works, non compressable is better. for most ccr dives your tanks stay [fairly] full and neutral, but when you need to breathe the gas, you can ditch the foam. This also helps to give steel sidemounted tanks that nice floaty arse up trim needed for long distances :-)

John