model the skirt to your character. Make sure it is welded.  (looks like it is)

Import it as an obj with nothing checked.  The skirt should look just like it does in MD.   Don't add any other items unless they will collide with the skirt.

In the cloth room, Set the sim, Set the collide against.  I like tight settings...  .2 or .3 so the clothing fits.

Scroll down to  Dynamic Group > click edit constrained group

Which gives you this:

---

If you were nice to you, you can Add  > materials  and choose the waist band.  otherwise, you will have to use the plus mines tools to add polys to the constrained group.   Poser will select polys you don't remotely want selected, so double check that from ALL angles. 

Items in the constrained group stay put.

Have fun!

;>

Andy!