What about the time between when the deer died and when you actually begin the 3 hour drive? Unless it was at least in the 40's, I would never try driving even one hour home with ice in the chest cavity. Also, the skin and hair on the deer insulates it so it needs to come off if it needs to cool quickly. If it's >50deg, I would quarter out and pack in ice for a 3 hour drive. If it's <40deg, I would prop the chest up with a stick and pack it with ice and make sure it's not right above the exhaust system of your truckThis is not absolute and I'm sure some folks who hunt out west will have more advice here shortly.