One thing that nobody has really touched on is that mini-fridges/freezers are insanely expensive to run. It will definitely cause a significant increase in electrical bills, and your roommates might be rightfully upset about that.

I would suggest a solid colored tupperware container in the freezer. If they don't have to look at them, they may become a little more receptive. Also for some reason the tupperware seems more secure than a paper bag.