I've stuffed the cavity with a bag of ice and kept in the back of the truck for up to 4 days in warm weather with no problems. It's important to gut it quickly and ice it soon. You'd be amazed at how long the ice lasts. Meats cold when it's butchered. Truck bed is covered and I make sure it stays in the shade. Keep checking the ice.

I guess the fat on the deer also keeps the cold in as well as out. It is it's own cooler.