Just a thought to update the Supply Chests treasure table with challenge mats.
Perhaps if that roll comes up you gain 10*(Level of Supply Chests) or something like that. [Note I'd like to make it so that if a level 20 opens a level 5 chest they would be penalized but I'm not sure how to construct that in mathematical terms. Perhaps it wouldn't even be needed.]
Certain challenges have many chests but are long and yield a poor material:minute ratio. Might this mitigate that somewhat?