just before you cut your pleats make sure you have a strong line of stitching in place holding down the pleats, this is one of the major support structures of the kilt, and if not held down firmley will just burst through wearing, then iorn on an interfacing of sorts just pleating it as you go along to keep it in line with the top of the kilt, then a harder canvis should be put on top for better support, sew on the widest part first which is at the hip line, then cut slits from the top down till the canvis lies flat, then continue to sew on by hand, same hard canvis should be used for both aprons,
good luck