I don't know why I never thought to drape my extra fleece up over the back like you do. I didn't have enough coroplast to do the sides of my upper level, and an idea like this would at least keep hay from dropping down behind the cage on that upper level.
Great idea! Also, I love the hay rack (a bent grid, right?). I might have to steal, errrr, uhhhhh, borrow this idea too.