That looks fine. If the air filter starts getting clogged, the yellow line will move to the left indicating that fact. With both of my coaches (my '08 and now my '14) I have never seen the gauge move very much. With that said, you should change the air filter every 3 years because they say that the glue holding the paper element inside the canister has a tendency to deteriorate and it could come apart.
Tom and Margaret
2014 Berkshire 390bh-60