I am a minimalist when it comes to quilt hanging systems. I have used round extension rods (curtain rods) resting on big nails for a very long time. The problem with round rods is that they can sag in the middle if the quilt is heavy. Flat rods work best but they can fall forward when they rest on the nails. It finally occurred to me to drill a hole in each end of the flat rod!
I used tension rods because, once you pull them out to the right length, they stay put (mostly). Use a drill bit that works on metal. If there are sharp edges around the newly drilled hole, file them down (or hammer the sharp edges).
A finish nail through the hole holds the rod in place.
I make my quilt sleeves a little shorter than the quilt so that the ends of the rods and the nails don't show.
The quilt lays flat on the wall and the rectangular rod doesn't sag!