I find that most people overthink things, but here is all I do.

I get a clamp skirt/pant hanger. I fold the kilt and fasten it, as if it were being worn (in other words, I close the aprons and buckle them together, or if I don't actually buckle them, the kilt is laying as if it were buckled). I think fold it in half again, with a verticle fold, with the pleats on the outside of the fold. I clamp the hanger on the top, and simply hang it like that in my closet.

Now, keep in mind that most of my kilts are 4 yard kilts (box pleated, of course!), and I have a 36" to 38" waist, so when folded in the above manner they fit in a single clamp hanger perfectly.

But the 8 yard kilts I have also work just as well in this manner. The only one that doesn't is a kilt I have from an extremely heavy Harris Tweed that I just simply don't fold in half, because there is no way the clamp would fasten down on 6 layers of the cloth. However, this is just the one kilt -- I have other Harris Tweed kilts that are a more standard thickness, and the usual method works well.

I don't seem to have a problem with moths where I live, and I wear all my kilts regularly enough that moth holes really don't seem to be a problem, so I don't take any extra precautions myself. Those that do worry about moths, though, please take precautions, and remember that cedar smells better than moth-balls! (Just remember to change the cedar out every year).

Aye,
Matt