sewingmom wrote: I think the heavier twill fabric will be bulkier and may need more length in the elastic than if it were a lightweight giingham.
I don't think the heavier fabric will need more length than you planned, it will simply droop. I have found that heavier fabric required heavier weight elastic. The button hole elastic is quite a heavy weight and should work, however, if not available consider a less stretchy and heavier band for heavier fabrics.
Let us know what works.