The thing is relatively rigid ABS plastic, so, if you put it into a tube, it would need to be fairly big diameter to account for its width and the fact that it is curved. My sister mailed me one years ago that was flat with a double thickness of cardboard around it. Not sure how much it could bend before breaking, but think that it's a fair amount. Shipping international is a combination of weight and volume, a tube would be significantly more volume, and, if it was strong enough to not bend, up the overall weight quite a bit. My shipping experience is a quantity of one, so may or may not reflect anyone else's results!
This used to be a BMW part in the UK, and it was actually cheaper through BMW than it was from the manufacturer. No longer see it on the BMW-UK accessories list, but it might still be there. The factory offers it in four colors...BMW only sold it in black, which is what I wanted, anyways.
2011 535i x-drive GT, 2014 i3 BEV
Soon (hopefully!) A 2021 X5 45e will replace the above