We live in the Twin Cities and store our Class C indoors (we're not winter campers or snowbirds). The best deal in the Twin Cities is the State Fairgrounds (info is available online). They only store motorhomes and cars (no travel trailers or boats). Their buildings do not have mice in them. The rate is very reasonable. You must be in by late Oct (they set very specific dates for moving in) and out in late March. We have found more flexible indoor storage but it is in Pine County - very reasonable but we can come and go as we please. No problems with mice. Subjecting any RV to the elements in a Minnesota winter simply can't be a good thing. But many do store outdoors. Just not us!
Todd