I've been thinking about a C&C cage too. I have guinea pigs, and I think that there would be a way to make this work, especially taking inspiration from the Closed Chambers thread. You could even add in a waterproof lining, like I've seen some people do.
Not in Minnesota, but I'm in Iowa. I just got my first tortoises, and I have mine currently set up in the (finished) garage, where humidity and temps stay perfect with this hot weather we're having now. I love seeing other folks' setups from similar climates!