IpSec and Gateway Failover groups

[Brentd27]

I have two gateways set up as a failover group with one set as Tier1 and one set as Tier2.

I have 2 unique DNS servers setup for each gateway under System->Settings->General.

I'm using the Legacy tunnel settings for point to point VPN.  I'd like to know how I need to configure my tunnels to automatically switch when the gateway switches.