Thanks all for the comments. I wonder whether the rgb and the Ha images should stand alone without any attempt to combine them... Or maybe I should just get better at processing..
The ZWO Ha filter does make things difficult with the strong reflections around the brighter stars. Does anyone have any experience with the Astronomik 6nm Ha filter versus the 7nm ZWO Ha filter (I'm using the ZWO ASI1600mm camera)? I notice Bintel have the Astronomik filters available.
Kevin