I do not think you should look in in the RRCs for the problem, it's probably the router settings at the radio end router. You have to setup port forwarding correct in the radio end router, be sure SIP ALG is not activated if the router has a setting like that. At the control end box you only have to change SIP contact to the public IP of the Radio end router ( which you say is now fixed). You do not tell much about what is not going ? Can you browse the RRC at the radio side so you know that at least portforwarding is working for port 80. Look at the status pages in both units when you have tried to connect there you can get some hint's about what is the problem. Dynamic IP.s is no problem, probably 99.5% of the Remoterig user have that.
73 de mike