I worked the rest of the project with the denim tube inside out. You can’t see it in this photo, but I tucked in about an inch on each side and sewed across the bottom of each leg.
I opened about 1.5" of the seam in the upper edge of the tube to make an opening for the drawstring and sewed down the two seam allowances.
Next, I sewed a ¾" tunnel for the drawstring and inserted the string.
Turning the bag right side out, it is finished.
Using a higher section of the leg, you could make one bag large enough to hold two shoes, but I thought it might be easier to pack a pair of shoes if they could be tucked into two separate corners of the suitcase. Just to keep this on the subject of vintage sewing machines, I sewed this project on my Singer 111W155 compound feed upholstery machine. That monster made quick work of those denim seams.
I traded an 8-track player for this machine in the early 70's. I had it professionally rebuilt for $295 and have used it for about 35 years now with no further repair. I expect it to last me the rest of my life.