Hm, yeah it must be the 'cool' part that causes the rot, because mine is wet all the time in summer, and so is Mj's - even more so this summer! I've only dug mine up once, to remove the two baby tubers, and the mama tuber was 4in. across then, and solid.
Keep that puppy warmer this winter and see what happens, Evan? Mine's in old, tired potting soil with a mulch of oak leaves on top and the pot is half sunk in the soil. Never gets much below 60-ish, I wouldn't think, and stays on the dry side i.e no water unless it rains on it.
