It is going to take more than insulation, it will take a heat source in that space.
Frost depth is typically 4 feet or more.
A lot of the unemployed people will not go there for a job because it can be dirty and hard work. Most people want cushy high paying jobs.
I know about deep frost, I lived in Wisconsin for some thirty years. A closed space needs only a 100-watt incandescent bulb to keep the pipes thawed, and there is something called a heat tape that does a most excellent job of keeping a length of pipe thawed in those few critical hours in the coldest of arctic blasts when there is nothing between you and the North Pole except a barbed wire fence. Electric “milk house” heaters are also pretty effective in still air. Heat rises in a closed space, cold does not. The secret is to prevent any heat loss by air exchange.
My cousins, who live a few hundred miles due west of there in NE MT, bury their water lines at 6’ to prevent freezing.