Hi @Jhans,
I’ve moved your post here, because it’s on the same topic.
This isn’t something I’ve had to set up myself, but it’s definitely possible. I’ve used a system like this before, but that one was intended as a service, so is a bit more complex than would be required for just normal control.
MAVproxy is a proxy for MAVLink messages (which are used to send control messages to the ROV, and which the ROV uses to send telemetry). That’s likely lower level than you need to worry about, because the onboard computer on the BlueROV2 already handles MAVLink messages and the video stream over UDP.
As others have discussed above you’ll instead just need some sort of router and 4G module at the surface (can be a floating buoy/surface vessel, or fixed to a structure) that’s able to support an external connection, and forwards the relevant ports to it 