Treat them like a tender flower bulb (ex, cannas, dahlia, gladiolus). I'd wait for them to go dormant before digging them out. I'm not familiar with Wisconsin fall and winter temps, but I'd guess by mid to late November would be fine. Dig out the crowns. You won't need to get every root and rhizome just get the main crown. Let them sit out for a few a week in the open air. This gives any cuts a chance to callus over. Then either pack them in cardboard boxes/ plastic crates with saw dust or shredded paper and leave them in the garage. Ideally they stay in a dry (no free water), humid, and cold place.
Alternatively, if you have extra space in vegetable garden or flower bed, you can dig a trench and bury them in the ground 6-12 inches deep, then mulch them. I would use a good tag to mark where the plants are. You can also mulch over top of the crowns to add extra insulation.