While working on the seat portion of the pattern I realized that I would have to rethink my strategy. I was originally going to have just one long piece of material span the entire length of the couch, but the two end sections move independently of the rest of the couch so I will have to create separate slip covers not only for each of the backs but for each of the seat areas as well.
Also, I'll have to include the arm sections in with the seat patterns for both ends as the arms move with the seats. Not an impossible task, but it does make things more challenging. I guess that's why this is a crafter's challenge!
I'll try to post some sketches of what I'm thinking is the new plan of attack later this week.