Marine GPX Course to Fenix or Quatix

Has anyone managed to get a GPX for a marine course on to the Fenix (6 in my case - same watch as the Quatix).

I have the Bluecharts downloaded and installed no problem via Garmin Express. I can export GPX files from any app (Active Captain, Navionics, etc) and share with Garmin Connect. You get promoted to create a course (only option that's relevant being other), however it will not save - my guess is because all the waypoints are in the sea, therefore it can't route it and has a fit. I have no problem if the courses are on land. I have tried to export a course from Active Captain to Connect with the start and end close to land and it manages to do that - but changes the route to be across land, ignoring my waypoints at sea.

This seems like a major omission considering the marketing around the Quatix - I've documented and raised with Garmin but had no response.

Has anyone worked out a way to get a marine course onto the device?

Cheers

Tom