It’s amazing how well things work when you follow directions.
Originally I had a separate virtual disk attached to the Seafile VM to hold user data. I’ve since axed that, and created an NFS share on my host machine to receive user data. No need to keep making larger and larger virtual drives. Files dumped into Seafile are poured directly onto host metal, which currently has ~6.3T available.
The Seafile client has an issue with the letsencrypt cert i’m using. Checking ‘Do not verify server certificate in HTTPS syncing’ did the trick.
Pro tip: If you’re using KDE, the Seafile client configurator is hidden under the “Status & Notifications” menu in your system tray.