I would suggest that you place each camera in a Ziploc bag with 3 or 4 small packs of silica gel and express as much of the air as possible when closing them. Very carefully clean all camera surfaces and remove all batteries before storage. Once a year, check the bags (without opening them) to see if the gel packs look like they need replacing. I also agree about the cases. Leather can harbor a lot of bad stuff and if it goes south, it can ruin the camera where they touch. All of the Ziploc bags can then be carefully stored in large plastic bins with perhaps a bit of foam padding between cameras. Expect that shutters may freeze, lenses may become stiff, and bellows may dry rot over time...

- Randy