[xrd]

Very, very, very infrequently. These are VMs that I will upload once and then not think about them for years in case my local machines die.

[electroly]

You know your requirements better than we do, but at first glance this appears to be a mistake. You can see what's going to happen: when you go to restore the years-old VM backup, everything is so out of date that it doesn't work and the updates fail. "Do it once and forget about it for years" is essentially always a mistake with backups.

[activiation]

A few years old VM might break when you update it if you ever have to restore it.

[Dalewyn]

Buy a HDD, backup to it, then put the HDD in a safe deposit box at your bank.

[sgc]

In which case a hdd + bank deposit box might be cheaper than other solutions.