Yep, Rocky, the main reason I've stuck with Priority Mail is for the free boxes! Now that I can print out labels online and have my regular mail carrier pick them up, this method wins hands down.

The "garment boxes" are roughly 12x13x3 inches. You can request them online, and they'll deliver them in packs of 25, right to your door. After I experimented a little, I found a way to fold the kilts so that they fit pretty nicely.