Come to think of it, it would be better to run the sshfs command in rc.local through systemd-run. This way the ordering on network.target can be properly declared (= no need for the sleep line) so that it will also be reversed when it’s time to automatically unmount during VM shutdown. For example:
systemd-run --service-type=forking --uid=user -p Wants=network.target -p After=network.target sshfs ...