The beaver carcass I have seen put out haven't been boxed up. They were in a metal bar cage with just larger enough openings so some of the beaver was available but the bear couldn't get the whole thing. The cage would allow the wind to carry the scent away to bring in the bear and was a high enough up that you judge how large a bear it was by how tall it stood.
Around here a used barrel can be bought fairly cheap then cut the top off and hing it. But I bet money the bear will tear it off before the weeks up. The last outfitter left the top off and put enough logs on it to make the bear hang around and it works to distract the bear while working to uncover it.
Barrels make for a good yard stick on how tall that shoulder is on mr. big.