After I had my chassis milled, I couldn't find foam that would keep the batteries where they belonged. So, I cut a small strip of Kydex (plastic bumper stuff) and double side taped it to the chassis to keep the battery closer to the centerline.
If you are looking into milling the chassis, it is definitely time to get rid of stick packs. Build your side-by-side packs and you will be much happier.
Jeff Gilligan