Neat stuff.
Are you using a Navio at all or just the R Pi and an arduino with ROS?
What are the latest thoughts of ROS vs a Navio2 ardupilot type of solution?
There’s an active discussion in the technology section of Thecombineforum.com that is exploring auto steer systems. You could contribute a lot to that. Look at low cost RTK and AgopenGPS threads.