I've been musing on the idea of a heavier duty lid than tin foil for this and I wonder if perhaps an appropriatly sized lid from a can would do...of course you would need to use a side cut can opener like a Pampered Chef can opener.
Oddly enough, back when I usta do Civil War reenacting, everyone carried a 4"x4" tin cup exactly like the Imusa alum. version and I made the exact same mod with a bail handle. Best mod I ever made to my stuff! Good job.
Never moon a werewolf