Just make the pleats as regular knife pleats, just like the instructions in Barb's book, only much wider (1/3 the sett size is ideal). Then, once all the pleats are sewn in, you'll want to open them up on the inside to make your boxes. Pin them down like that and sew them in place with a line of straight stitching across the top of the kilt. You'll also want to baste them in at the fell line and again about half way up from the fell.

Clear as mud, right?

M