I didn't have any stiff 'muslin', however, this is just a toile to test the pattern.
1. I cut the pieces for the frills individually and cut the foundation piece doubled
I made facings for the hems for a bit more stiffness, but they can also be 'grown on' to the pattern pieces.
I sandwiched the bottom frill between the double foundation pieces to hide the seam allowance of the bottom frill
When turned out the bottom frill protrudes
2. The second and third lowest frills are sewn in place on the foundation piece with the frill heading facing down, the fourth is sewn in place with the frill heading facing up
3 The fifth and sixth frill are sewn in place on the foundation piece with the frill heading facing down
The waist tape is sewn on from the wrong side of the foundation piece
4 Waist tape is flipped over to right side and hand sewn down.
Tournure ties around waist
(This is a toile and by no means is it an historically accurate construction. It can be used if you are experiencing difficulties with making your pattern)