It seems quite difficult to guess who's owning the share as the uid/guid 's mount point aren't representative enough.
/opt/backuppc being the mount point ...
ls -ld /opt/backuppc/
drwxr-xr-x 9 root root 4096 Mar 2 18:59 /opt/backuppc/
but once drive is mounted ...
ls -ld /opt/backuppc/*
drwxr-xr-x 10 backuppc backuppc 4096 Feb 26 16:00 /opt/backuppc/files
In that case, you won't be able to guess the correct owner.
Additionaly, several users might share the same "usb volume" and this is why the suid is so helpfull.
Same problem with fstab, as it has no clue of what params/ownership to give to the partition.
The easiest way is probably the "personal options" within panel/db.