You did a nice job on this ( I couldn't have myself). You should at least keep your curves, or outside edges grouped for later use of tries. You group them but edges remain if you also want to merge the geometry. Later exploding a copy of the curves will place the edge back in the softened geometry. From what I see of Jeff's and other's work, you use a lot more faces, and maybe that's not necessary. I restored and tried your center piece. Someone more experienced might be able to skin it.Untitled.skp
and here's an attempt but it still shows little creases in the middle.attempt.skp