Fridges will work . . . but for regular use, I like my HDDs in mobile racks (now with triple cooling fans) in a full tower. That puts them up in the 5.25 bays away from the mobo and CPU heat. They are individually cooled that way and also give you the bonus of having on/off power switches for them so you can select a drive.
That gives you many choices for different OS's on different drives, or system backups that are just a un-lock, swap and lock away. (Takes about 2 minutes to shut down, swap drives and reboot.)