I would put them in cold storage with the wallets stored on usb sticks, splitted in 5 bitcoins each pendrive.
That's stupid, unless you have multiple backups of each flash drive.
Just store it all on one flash drive and back the same wallet up onto 5 or so more mediums of storage. Keep an unencrypted copy or two and encrypt the rest. Send some of the encrypted ones to relatives/very good friends.