I have a route plotted fine on using DirectionsRender but I cannot find out how to replace the generic Google markers with my own.
I know and use this in a normal Google
The DirectionRender takes an option called markerOptions. Quoting from the API docs:
All markers rendered by the DirectionsRenderer will use these options.
So, if you want to set the markers use MarkerImage (as philar has indicated).
Your other option is to pass suppressMarkers: true
to the DirectionRender
's options and then simply use your own markers.