Thanks for your help with this.
I updated the fstab to the following: 192.168.20.22/NUC-backups /media/NUCBackups cifs credentials=/root/.smbcredentials,uid=rob,noperm,rw 0 0 but still get mount.cifs: bad UNC (192.168.20.22/NUC-backups) as the error. If I enter 192.168.20.22 into my web browser it takes me to the OMV admin panel so that's the correct address.
What else might it be do you think?
UPDATE: Here is the share setup in OMV: