Shorewall users - Jan 2012 - multi-isp dynamic connections - is shorewall right for this?

Hi everyone.

We are putting together a network appliance for emergency management
use, and it has to be
adaptable to different network connections.
eth0 is a connection to whatever physical ethernet is available on
site, if any, including satellite.
ppp0 is a 3G modem connection, if available
br0 is the internal network supporting IAX2, SIP, general internet use
and video monitoring, over
eth1 and wlan0.

When the system is started, there may be 0, 1 or 2 possible network
connections available,
and if there are two, then eth0 is preferred over ppp0, which should
be shut down if it is active.
All of the possible external network connections will present as
dynamic addresses,
using dhcp on eth0 and ppp on ppp0.

I am looking for a firewall/failover system that will route/filter ALL
traffic between br0 and whatever external
connection is available at the time, failing over between eth0 and
ppp0 as required.

Does this sound like shorewall with lsm, and if so, any hints/gotchas
before I tear out what is left
of my hair.  The linux platform is Voyage One, which is based on Debian.

thanks
Ross

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