[Serusers] rtpproxy question

hi all, I am trying to run nathelper with rtpproxy, and I am currently using a configuration based on a supposedly working standard example config, but I haven't got it to work yet. I took a look at an example configuration for SER as an application layer gateway,between two RFC1918 networks, and noticed that rtpproxy was called with some parameters in there (i.e. force_rtp_prpoxy(EI), obviously denoting the direction from External network tow an Internal one) Does anyone know if these parameters are mandatory? Or if someone has a currently working nathelper/rtpproxy configuration, please provide any feedback on that. I also keep getting a "cannot extract body from the message" error from the rtpproxy. Cheers