.. A better solution for the waistband for both those SW pants is to use 1" non-roll elastic (see photo) . For the length, I cut mine an inch less than recommended for my size for the stretch part PLUS another 8" for across the flat front portion. I then insert the elastic in the casing, stitching it down at each end, leaving that part of the elastic unstretched inside the casing across the flat front because it stabilizes and keeps the front of the waistband from creasing unattractively. ..
Thanks for the hint. This is so much better than trying to stabilize a portion of the waistband!!!