On my White Hawk the glacier package consists of a furnace duct to the underbelly and a can of spray foam surrounding the hole the tank drains come through. The plastic underbelly doesn't have any insulation on it. The fresh, black, and gray tanks are all in a "heated" space technically. I've had mine out down to 20 at night but I think zero would be too cold.
2016 Jayflight 27bhs Elite
2015 Chevy 2500HD