[Serusers] Asterisk inside a NAT, client inside ANOTHER NAT

Hello, By looking at this section from the link http://www.voip-info.org/wiki-Asterisk+SIP+NAT+solutions 9. Asterisk inside a NAT, client inside ANOTHER NAT In this case, we need a middle man to even find each other, an outbound SIP proxy that handles the SIP transaction and is reachable by all parties. To get media streams from point to point we need another middle man, a media server. Asterisk could be that media server, that could add media codec conversion. Portaone's rtpproxy works together with SIP Express router as a media server in this situation. Could anyone share the configuration on how to do this ? I could only succeed if I put on port forwarding on the UA's end. Regards, C.K