Hi Philippe,
I think this is a remarkable image, at least from the documentary point of view. You brought out extremely well the external H-alpha shell towards the north.
One small note: There is a myth that says that the H-beta emission is just the same as the H-alpha emission but with lower intensity... That's just a myth. Some times you can find completely different structures in H-beta and H-alpha. So putting the H-alpha information as H-beta in the G and B channels is not giving any "real" information to the viewer. A completely different thing would be that you don't want to represent the H-alpha emission as pure red.
Best regards,
Vicent.