I've written (but not yet published) a novel based loosely on my experience as a JW. I invented my own religion for it, for several reasons. For me the most important factor was that I didn't have to worry about the details of life as a witness, I can put words in the mouths of my characters without having to worry about whether or not a JW would say that.
I'm currently working on another project by I hope to get back to this one soon. Basic plot line: Armageddon hasn't arrived so the religion decides to take matters in their own hands.