Cut your fabric pieces.
The PUL rectangle will be the front/top of the envelope pocket to prevent front-leakage.
Assemble faces-in before sewing around the edges.
Sew all around the outside and trim your corners before turning through your pocket opening.
Turn through the pocket. For ruffled legs and back, top-stitch all the way around (THEN add your elastic casings and elastic. For non-ruffled, just sew your elastic casings and install your elastic. Then top-stitch last.
Elastics and wing snaps added.
Snapped to the middle rise and stuffed with a snapped-down BG insert.
Showing PUL on both sides of insert to prevent front leaks.
Templates can be downloaded here: http://prefold2fitted.blogspot.com/2012/10/online-free-downloads.html