[CentOS] How to preserve iptables when running the GUI tool ?

Hello

I have set up NAT with iptables for an openvpn connection, so that the 
VPN server could give VPN clients access to the entire sub-net of the 
server.

The probelm is if I start system-config-securitylevel to say disable the 
firewall, and then again to enable it, my iptable rules are gone !

I did run `service iptables save` before.

Is there something I can do to prevent this ? Is there a gui interface 
to enable NAT over a VPN connection that cooperates with 
system-config-network ?

Thank you,
Timothy Madden