About a year ago, a man sent me a military box pleated kilt that had been rumpled and stuffed in a bag in a closet for a long time. It was very heavy weight Black Watch. I pressed out the pleats below the fell, down to the bottom of the kilt. Then I carefully aligned, positioned and pinned each of the new pleats. Instead of basting across the pleats as in your photo, I basted each pleat vertically down the length. As in your cross section of the bottom, each pleat involved 4 layers of heavy wool, plus the thickness of the pleat underneath. To press the pleats, I left more wetness in my press cloth than usual. I make no claims at all to be an expert on military box pleated kilts, but this system worked and the customer was happy with the results.