All of my obsessive-compulsive behavior has paid off. I finished the main portion of the needle roll and felted it over the weekend, and I must say, I'm pretty happy with how it turned out. Here are the before and after pics:
I threw the pen on there to give some sense of scale, and as you can see, the felting process shrank it up quite a bit, although most of the shrinkage was in the length, not the width. It went from being approximately 24 inches long to just over 17. After I took this picture, I also stretched and pulled it a bit to get it to be more squared off in shape.
Now I just have to knit the cables to stick the needles through and then sew on buttons and it's done! I'm just hoping I have enough yarn.