Am I doing something wrong with layer masks?
So I've created a layer mask, I have it selected, but when I try to draw on it nothing happens and no marks are made. Did I miss something or is there a possible reason I can't doing anything with the mask?
In your screen shot it looks like you have the mask selected but for those who don't know, you have to click that mask thumbnail to paint on the mask.
Masks in CSP work opposite to how they are done in PS. Instead of painting using opaque pixels to mask the layer, you need to paint in transparent pixels to hide. Opaque will reveal
Ah, that's what I was missing! Working as desired now, thanks.