RouterA:
Interface tunnel100
IP address 10.0.0.2 255.255.255.0
Tunnel source {RouterA WAN}
Tunnel destination {RouterB WAN}

RouterB:
Interface tunnel101
IP address 10.0.0.3 255.255.255.0
Tunnel source {RouterB WAN}
Tunnel destination {RouterC WAN}

RouterC:
Interface tunnel102
IP address 10.0.0.4 255.255.255.0
Tunnel source {RouterC WAN}
Tunnel destination {RouterA WAN}