I like Arizona Sunrise's idea of the tabs. I would use a light lowloft poly batting (for the insulation quality) and a backing.
Another idea for the top would be --that's if you don't mind making holes in your "quilt" -- use those large gommets that are all the rag in window treatments. That would slide well over your rod.
Another thought: what would be wrong with making it the same size as the door.? Who doesn't like seeing a beautiful quilt hanging on the wall?Good luck. Happy quilting. :lol: