@jprobins 

  @jprobins 

I don't want to 'muddy the water' here but have you considered switching the RS700 to 'access point mode', that will put everything on the same LAN subnet and all the port forwarding is done in the ER707. If you want to keep all the devices on the 192.168.1.x subnet, then just change the ER707 Lan to 192.168.1.x.

If you've got DHCP reservations on the RS700, then they will need transferring to the ER707

  @MisterW That may be where I have to go in the end, if I cannot figure out the double NAT issue, but I would like to avoid it if at all possible.

  @jprobins 

I assume you've still got the port forwards configured on the RS700 as before ?

One thing worth trying is to configure the DMZ on the ER707 to be the RS700 i.e 192.168.0.102 and then you dont need any specific port forwards on the ER707.

I wouldnt normally suggest using a DMZ since it forwards everything to the destination, opening it up to the world. However in your case the destination is a router with its own firewall so that still gives some security

I finally found my error. Turned out to have been a simple mistake. All is working now. Thank you for all your help. It was greatly appreciated.