I'm going to pick up my first batch of chicks this Wednesday. The forecast for that morning is about 20F. The drive will take about 45min-1hr. How much do I need to worry about keeping them warm in the car on the way home? I was thinking I should bring some of those chemical hot packs to put under the box, as well as keeping the heat turned up in the car. I told my husband I'll stuff them all inside my down coat if I have to any tips?