Re: Put a heater in the safe then ?
We had a similar problem with 8" drives. We decided it was the drive, not disks. The horrid Apple II 5.25" floppies and drives not affected (early 1980s). We put an electric convection heater turned low in the room.
Similarly forty PCs built (mid 1990s) in a cold warehouse didn't work on site till HDD reformatted and OS reinstalled. Solution was to keep HDD stock in the office and do final fitting and install there. Which suited me better. Could take off coat!