I came across this today and it’s an interesting idea! While I’m not sure I endorse creating and maintaining a tunnel, especially as root, I’m sure there are use cases where it makes sense. If nothing else, defining the config files and their contents to create a service is worth seeing. All the details, including how to make it run after reboot are at https://medium.com/linuxstories/linux-how-to-create-an-ssh-tunnel-as-a-systemd-service-73e6e0fff19b