Place potatoes in a Dutch oven, adding water to cover. Bring to a boil; reduce heat and simmer, uncovered, until tender, 10-15 minutes. Drain; return to pan. Mash with cream cheese, sour cream, butter and milk. Stir in bacon, cheeses, onions and seasonings. Cover; refrigerate overnight., Transfer to a greased 3- or 4-quart slow cooker. Cook, covered, on low 3 to 3-1/2 hours.