-5 is no problem. In MN and IA they'll have winter blended fuel you'll want to buy. Add the labeled amount of treatment and you'll be fine.

My Duramax has no problems with the cold. I normally run it in the shed at night but don't have the option if we go out snowmobiling. I run straight 2 with treatment if the lows are above 0-5 degrees and usually about 30% #1 down to -20.