Hi Pete,
Sorry for the delayed comments!
Yep, you do it right. The workflow is just to put the SIM card to the Reach RS2, and access the device via static IP. However, before that, you need to go to the Reach Panel and turn off the Protect Reach from being visible from outside the local network option. To access it, go to the Reach IP in any browser and tap the gear icon.
Please keep in mind that Reach RS2 Wi-Fi doesn’t have a firewall. So everyone who knows your static IP will be able to connect to your receiver.