I got past the MariaDB Host error. In the config I switched to advanced view and then added an extra parameter (--add-host mariadb:x.x.x.x) replacing the Ip with my UnRaid host IP.
Also for the MySQL host parameter I clicked edit and changed the key name to MariaDB and I entered the same IP - the UnRaid host IP for the value.
The log then showed that MariaDB was foundMariaDB hostname found in /etc/hosts. It then showed errors for redis which I think is the same issue but will try that tomorrow.