In a large mixing bowl, combine onions, mushrooms, water chestnuts, stuffing mix, herbs, and spices (sage through pepper), and stir to combine. Pour the melted butter and vegetable broth over the top, and mix thoroughly.
Grease the bowl of a large 6 or 7-quart crock-pot with non-stick cooking spray, and spoon the stuffing into the bowl.
Cover, and cook on low for 4 to 10 hours.
Notes
The cooking time really can range from as short as 4 hours to pretty much as long as you need. I've cooked it for about 10 hours before and it was great. Just give it a stir, as some of the bottom parts will be a little browned and crispy.