I have a Netcomm NB16WV-02.
So of course, first things first, when you set up your router, you need to add whatever your DNS addresses are. For me, I'm with getflix and the closest point is Sydney so I set my DNS under ntetwork settings -> DHCP server to (but yours will be whatever your DNS uses):
Primary DNS: 184.108.40.206
Secondary DNS: 220.127.116.11
Then you have to connect your chromecast. Chromecasts at this point in time only connect to 2.4GHz networks, so if you turned your 2.4GHz channel off, you need to turn it back on (under Network setup-> wireless 2.4GHz) and connect your chromecast to it (go to your chromecast app). After a reboot of the chromecast I had no problem with the chromecast being on the 2.4GHz network and me being on the 5Ghz (ie. there is no wifi isolation).
Ok now you just need to stop the chromecast from accessing google's servers. For some reason this is essential, whereas it wasn't on my BudLite.
Go to Advanced settings -> Routing. Click enable static routing. In the boxes type 18.104.22.168, 255.255.255.0, and then the address of your router. In the next box down do the same but with 22.214.171.124.
Now reboot your chromecast. It should be working now.