for some unknown reason Zerotier stopped working for me. I searched for an alternative and finally found Tailscale. https://tailscale.com/
It provides the same p2p network service as zerotier, but it uses wireguard to connect the nodes together. Installation and setup was even simpler than with Zerotier.
I got it installed and running on my desktop, laptop and rovers in 15min.
Telemetry and video from rpanion-server to my desktop PC worked immediatly after adding the endpoint to rpanion and entering the video source in Missionplanner. The rover was connected to a 4g mobile hotspot and my desktop to cable internet. The video (640x480@1000kb/s) had no perceivable latency. I am not associated with Tailscale in any way, but for anyone interested in unlimited range/mobile connection to their vehicles, it is worth a look. It is free for single user/private use.