Ah looks like I was making it harder than it needed to be, thought I had to combine them using a merge shader but looking at Bobby's file I can see that chaining them works great.
I was battling with this for a while last night, should have just asked you guys
Thanks.
mhaze, I did try using "add" that sounded like the option to use but it didn't work. Not sure that the merge shaded can be used for this sort of thing.