Kevin, W0KCF,
Have you seen the official Wiki at: http://wiki.ampr.org/wiki/Ubuntu_Linux_Gateway_Example ???
Feel free to ask here. Quite a few of us reading have setup gateways on dynamically assigned WANs.
Also, I do see one problem...if this is a Ubuntu machine, there's no tunnel interface under ifconfig. What device is running the tunnel?
- Lynwood KB3VWG