I concur on don't let them pack it for you. Every time people I know did that with audio items it was a bust.
I've sometimes had luck getting big boxes from appliance stores for things like speakers. If you look around their scrap, you can even find rigid internal inserts that are handy for the side where the drivers are. I'd cut down to fit snuggly what I had and more or less make the box. With a little bit of looking at it I don't find it hard to do. I use tape on all seams. And always double box.
Oh, and for the person you are sending it to, label which side the drivers are on as well as top and bottom. That way they aren't in danger of slicing open things where they might slice a driver as well.