Thanks for the comment,
First look on their page I see "You may need to Open a Port...."
That pretty much indicate's that it's not gonna work behind CGNAT.
I did have success with RealVNC & their Cloud service, where the host calls home & then notifies of the ports it using to get out on,
but that entails running the GUI & although I didn't initially have an issue with that, I''m starting to see that GUI, VNC & then CMX is too resource intensive for the pi3-B I intend to use.
Reverse tunnels seem to be the way, but that's still something I'm trying to understand.
So many varying examples when you are still vague on the base concept.
So current status is the Ecowitt has been installed 50km away & the rPi-3 still sits back here.