Here is the reference for GPS positioning.
Is it as simple as running external antenna from BR2 above water line?
Yes, a few of us have tried these modifications and a compatible GPS module plugged into the GPS port on the Pixhawk works. This was done back in the day (2016), but everything still works with the current software releases: Report on internally mounted GPS sensor
If I could simply view ROV position in Map View simultaneously with Ping Viewer data it would work for my immediate needs.
Ping sonar data (acoustic range) isn’t integrated into QGC yet, but you can set up both windows on your monitor and see both. Something like this:
