Hello Rami,
You have to create a static route 0/0 to Null0 "ip route 0.0.0.0.0 0.0.0.0.0 Null0". You can also put a boolean tracking to the SIG tunnels to uninstall the route if all the SIG tunnels go down.
Then, in the Traffic Data, you indicate in Action -> SIG in the last sequence.