I've used plastic cases with rigid foam. These are used and intended purpose was for some gizmo that no longer is sold. Recut or stuff the case with foam and place HDs as needed. A simple sturdy case with bubble wrap does fine too. You can make such or buy one with inserts by looking for "cases" for tools or shipping. look in military surplus or "special case" vendor like Pelican and others. these cases cost a bundle but they are very durable, shippable, waterproof, shockproof, instant ready and customized(if desired). -OR- visit a local h/w store, Lowe's, Home Depot and find a simple re-closable toolbox with your foam inserts you find and make. I suggest you use "ESD/static free foam". I believe vendors like Uline which provide shipping materials and such cases. As well as any electronics/surplus resellers may have them, used or new at reduced cost. google away
for my hard drives.
Instead of "backing up", I clone my hard drives. Much faster. I have three desktops and two laptops. The cloned drives are stored in anti-static bags. I want an inexpensive box, similar to a CD case (not that size of course) or such to store the drives in. Three 3.5" and two laptop drives. I've searched and searched but can only find active drive cases, nothing to just store the drives in. Maybe I'm not using the proper search term.