The modem has public external IP and DHCP server set in the 192.168.192 range, and eth0/0 gets 192.168.192.3 from the modem.
On the modem I have set forwarding for the ports from external ip as follows:
Src 3300/29328/55611, to 192.168.192.3 and dst 3300/29328/55611.
This setup worked when I had the ports forwarded to my previous router, before I replaced that with the SSG5.