Stumbled upon a fantastic video tutorial about using clipping masks to combine mono images. It is by Ken Crawford.
Makes a really big difference imho anyway.
Fullsize version here
http://www.astrobin.com/119939/
Image taken through ED80 with Atik 314L Mono.
15 minute Ha subs (60)
5 minute RGB subs (60 each)
Combined using method outlined by Rob Gendler and Ken Crawford
Thanks for looking
DJ Scotty