I'd forgotten I knew what these were
google images brought back the option of a jar and a box
http://speedkin.com/2009/11/28/my-diy-butter-bell/
but reading the blog made me wonder if you all are belling a pound of butter or a cube of butter.
I have a covered rubbermaid style dish that holds a cube and regardless of temp it never goes rancid.
Probably takes 3 days to use a cube. But a whole pound...might be a different story.