Actually, the other machine is RAID 1 and does get automatically backed up. Total cost was a few hundred $.

Temperature control is mostly irrelevant, as long as the temperature and humidity stay within the operating parameters of the drives. Two drives failing at once + losing a backup is also extremely unlikely.

I suppose everything could be taken out by a surge passing through the UPS box, or an EMP. Even then while the drive electronics would be zorched, the data on the platters would be recoverable. But that’s pretty much an impossibility anyway.