ZeroTier as a ReadyCloud replacement.

All you need to do is specify the ZeroTier IP address, which you can find in your ZeroTier account or with the ifconfig command via SSH on the NAS, instead of the "normal" one.  If you want to do it by name, you'll have to add a unique name and the ZT IP address to your hosts file.  While that's a plain text file, you have to edit it with admin privileges.  Rather than me explaining how to do that (which you may not even need), you can just Google it.  You can use that address for HTTP (including admin), SMB, and even SSH.  I was recently out of town and could do everything remotely except watch videos, and that's just because my home upload speed to the internet is too slow.  I had to download them and watch the copy locally.  If you use Plex, it can transcode based on transfer speed, but I prefer to see the full resolution using the extra step of downloading.

What I have done is add _ZT to the normal network names and put them in my hosts files.  So NAS1 is NAS1_ZT via ZeroTier.