Sally Jupiter Costume (Silk Spectre I) from Watchmen

Step 9 Belt: Preparing to sew, and sewing the central section.

I did the belt in 5 separate sections, I think it's possible that it can be done in three, depending on your body shape.  As I am a rather curvy gal, I made the belt in five sections to get the proper angle and ensure the belt would not come down into a V shape, as seen on the back of some wedding dresses and formal gowns. 
For the central section: sew the top two sides, the bottom two, and one of the others, right or left, your choice.  Leave one side open, with at least  a half an inch stitch down the top and bottom of the open side.  Trim the interfacing around your stitching, and flip the piece right-side-out.  Push corners out with your dull-pointed tool once again.  Decide which side you like better, and stitch the remaining parts of the open side.  It does not matter what kind of stitch you use here, I don't think, as long as it is stable, as it will be underneath the side pieces and will not show.  Stitch a row or two of topstitching all around the outer edges of this section for stability.