I am using a SUSe Linux desktop with a Fixed IPv4 address. The NAT can be configured to pass protocol 41.
Would I provide the 'external' IP address for the NAT as the IPv4 end point for the tunnel?
Yes the broker needs your real routable IPv4 endpoint, and using the "Linux-route2" example will require the internal, non-routable IP your NAT appliance DHCPs to your machine. Using the "Linux-net-tools" example doesn't require that you specify that internal IPv4 address.