I didn't realise about docker not being meant for production, I guess the mattermost-dev suggested name makes sense now! I've decided to stick with it because people are already signed up and using it though.
For anyone in the future, as I can't seem to access MySQL inside the docker container I've copied the entire /var/lib/mysql/, /mattermost and /config_docker.json directories and files as I've been asked to do application level backups. As you say docker can also export images.