Honestly, since SR2, I think Dawn is one of the easiest weight map figures to rig clothing for. The freebie above, I rigged when Dawn first came out and it was such a nightmare, I just trashbinned it.

With the advent of SR2, I tried the outfit again and it was a joy to rig.

The sitting position here? No movement bones, no morphs required. The skirt follows the pose with no extra posing required.