Hello,
@uzapm, I am working exactly on the same thing these days. Have you sorted out how to generate v1.0 messages? If I build apm planner with v2.0 MAVLink messsage headers, it fails. I created a post in this forum https://discuss.ardupilot.org/t/custom-data-sending-via-mavlink-protocol-dev/21343/2 and I put steps which I have done in the vehicle code, maybe you are missing something there, check it out.
I am stuck at building APM Planner with new headers, maybe we will solve this problem finally.
Good luck