Not sure how large your duffle bag is. I use a large "gym bag" when I travel. The kilts go right off the hanger to lay in the bottom of the bag. I do alternate the direction of the kilts if I have more than one.

If your bag is smaller, I've read that Utilikilts folds their kilts into 1/4 size for packing between their gigs selling at games. That is, folded as if on the hanger, then folded once more.

And, if you're staying at most motels there are irons in the room or an iron can be borrowed from the front desk.

And, if you can fit it in, a portable steamer will cure whatever wrinkling happens during travel - both for the kilts you've packed and the kilt you've been wearing.

Ron