I think its better to store your private keys .txt in usb with lock so that no one can open your usb easily.. or archive your private key in rar file and put a password so that no one can open it and save it in any folder with copy right protected or lock that cant deleted or remove any files inside the folder
.rar file is good but the password of a rar file can be broken, the better way is to export the private keys encrypted in the first place so that it can not be read by human and only be read by computer if you enter the password that you used for encrypting them.