I used the Redpine maps for Wisconsin although I probably should update since mine are from 2009. This season I got the Michigan mapping, which includes the U.P., from VVMapping and even though I won't be able to try them in the U.P. for another week or so they look very nice. With VVMapping when you purchase online you get the mapping downloadable right away, then a couple days later you will receive by mail a hardcopy of paper instructions and a CD copy of the maps and a couple extra mapping programs.
Just to add concerning powering the unit - I've powered mine from the sled with a 12V outlet and it works great. I've also used the GPS internal battery standalone with no power from the sled. However, it's worth noting that you should make sure the GPS battery is charged before you go out, whichever way you choose to power it since even when plugged into the sled the battery will not charge below 32 deg F. It will run the unit but won't charge the battery. Garmin doesn't say exactly why it's made that way but I can only guess it's due to the Li-on battery and it's chemistry. The battery can be charged (when between 32 and 104 deg F) either from the 12V plug or from the USB cable when plugged into your computer.