I would imagine people in MN might be more likely to have "four season" tents than people here in CA; that will help some. I don't want to increase your trash problem, but from my sojourns to Badger Flat (roughly a mile and a half altitude!) I can vouch for the 8-hour chemical heat packs ("Thermacare" is a brand name, often there are cheaper generic versions) usually sold for sore muscles and such. Under one's clothes or even in a sleeping bag, it's amazing how much they help.

And then of course, there's the big guns - propane heaters. Many are not safe to use inside a tent, but Coleman's catalytic heaters are. I have an older model and it works beautifully. (On camping trips, I generally use it just to ease the transition between being clothed and being in bed, whichever direction that's going - but it's certainly possible to use one to keep warm otherwise.) If you're involved with sanitation when it gets cold, you might need to consider a recycling drop off for expended propane cylinders.