I started the top this past weekend, and so far, so good. The picture below was before I attached the straps to the back, and before I inserted the elastic. I want the elastic casing to go along the bottom of the top-part of the dress, but I wanted to make sure I left enough seam allowance for the skirt. If you look you can see the two black marks for the seam allowance, and two black marks for where the elastic will be stitched on either side. In fact, you can see where I already attached the elastic on the left.
And here it is with the straps sewed in and the elastic added (though I haven't finished the top of the casing).
Next time I get a chance--the skirt!