I kinda discovered a way to cheat, with the backing.
First of all, I use Elmer's School Glue, for basting the sandwich together; I use Warm & White or Warm & Natural for batting.
Let's see if I can explain what I did, without causing too much confusion. Okay, I first glue-basted the front to the batting. Then I marked the center of the front/batting, top and bottom. I measured out the backing length (fabric A), then matched center top & bottom, to batting side of sandwich. I glued this to within about an inch of the selvage. Then I took my fabric B, for the sides of the backing, cut the proper length and cut the fabric vertically, making two strips (one for each side). I placed one side of B, right sides together, on top of A, with the raw edge even with A's selvage. I safety-pinned B in place, to prevent any shifting (pinned on each side of future quilting line, as well as a bit farther away, to keep B out of the way). Then I flipped the sandwich over and did one vertical line of quilting, at a point to catch at least an inch or so in from the selvage/raw edges of A and B. I made this line where I'd planned to have a quilting line, anyway. Flipped the sandwich back over, unpinned, trimmed the seam, then pressed B over to the edge of the batting and glue-basted into place. Repeated with other half.
