1. Go to http://plex.tv/claim/ to create a “claim code”.
  2. In Package Center, search for and install “Plex Media Server.”
  3. Make sure to select the “Claim” option when installing, not the default option! Enter the claim code you generated in step 1. Otherwise you’ll have to reinstall; I was able to sign in to my Plex account but then kept getting the error “Not authorized: you do not have access to this server”.
  4. In File Station, right-click the volume(s) you want Plex to read, click “Properties”, “Permission”, “Create”, then enter “PlexMediaServer” under “User or group” and check “Read” and “Write”.
  5. In Plex, click the settings wrench icon at the top-right, go to Manage > Libraries, click “Add Library”, then select the volume(s). In my case they were under “volume1”.
  6. In Plex, go to Settings > Network and click “Show Advanced.”
    • For “Preferred network interface”, select your ZeroTier network interface (e.g. ztabcdef (10.147.17.123)).
    • For “LAN Networks”, enter “192.168.0.0/16,10.0.0.0/8”.
    • For “List of IP addresses and networks that are allowed without auth,” enter the same.

You should be all set! Now you can stream directly from your NAS even when away from home, and you don’t have to expose anything to the public Internet.