Must be a fairly sturdy plastic milk carton to prevent the mech or hanger from getting bent in an impact?
No idea. Just a tip I picked up somewhere. You can pad the inside of the bottle out with a bit of card or bubblewrap. How hard are they going to hit it. I don't think anything will survive a lump hammer kind of thing, but for the pushing and pulling type of aircraft handling situations, could be fine. Anyway, worked for me up to now.