I just bought a "five-day", 54 quarts cooler, and I'm going on a trip that will involve camping. What is the minimum number of medium-sized ice packs should I put in there to make sure that the food stays at at least fridge-temperature for something like four days? The cooler will remain mostly in the A/C-cooled car during the day, and the cooler will be pretty full of food (some of which will start frozen). Would two packs be enough? The extraordinarily bright people on the Coleman customer service line told me "as many as you can", which doesn't help at all...