I finally got around to working on it at the end of January 2016. Creating the basic shapes in Inkscape was very easy. The fun came in when I started messing about with various filters to see what kinds of effects I could get. After a lot of experimentation I eventually ended up with this design.
In this tutorial I explain how to create this design using the simplest steps I can think of. My actual process was much more complicated and involved a lot of trial and error. (Please note: This tutorial is intended for instructional purposes only. I am not granting permission for anyone to use or publish this design in any form.)