My suggestion is to have ip route 0.0.0.0 0.0.0.0 18.104.22.168 after ip route 0.0.0.0 0.0.0.0 tunnel0. Because always routing is checked from top to bottom . If a match ( First route entry ) is found that interface or ip address is chosen.
We have configured the outside and inside Interface with official ipv6 adresses, set a default route on outside Interface to our router, we also have definied a rule , which also gets hits, to permit tcp from inside Interface to any6.
In Syslog I also se...