Asterisk calls forwarding


here is my senario that i am trying to setup.

I will get wholesale traffic calls (H323 with G723 and G729 codecs) from the carrier to my Asterisk system and the asterisk should forward those calls to the client gateway using VPN tunnel(IPSec).

My client is using Linksys RV042 router in the client side and I made the VPN using IPSEC and it is successfull. Now I am able to reach the client gw(cisco AS5300 series) using nat ip from VPN.

Now I need the calls to forward to the client gw. Please suggest me the best solution for my requirement.