Hi,
I have been discovering simple and secure way of protecting the Tor key files recently, in order to achieve the safety of the keys on VPS.
So I created a folder on Linux called /tor and it is stored in the RAM file system. I put my key file into that folder and link it back to the data directory folder of Tor. I also backed up the key files in case my server need to be restarted and the RAM would be cleaned up. I left the key in RAM for some undesired failures, errors or configuration which need to restart the Tor software.
If the server gets down, I would probably do the simple cut and paste in the SSH client to restore my key files. Or in a higher level way if cut&paste is not safe enough.