The long awnings, 18+ feet, will tend to bow in the middle just from the tension of the awning material itself. The roller tube actually bends inward. The center awning support helps with this a lot by pushing the center of the tube back out. Ours is 21 feet and I use one on our awning when we are snowbirding but don't usually put it up when just camping for the weekend.
Tension rafterThose curved rafters are really nice. Saw a couple of rigs at our winter campground that had them. Might have to think about those in the future.
Curved Rafter SupportsBarney