I agree. Cooling down the plastic first goes a long way to making the ice last longer.The biggest thing with any cooler is keeping it iced down. Leave a little bit of water in the bottom and ice it daily. If you go a couple days without use, ice it the day before or put it in the deep freezer to get the cool down process going.
I was really thinking about this for the up coming camping trip... I'd like to have some non-canned food for Saturday or Sunday, but I'm also not going to spend serious coin on a cooler for that.
And you can buy ice for $2 a bag within 300 yards of the parking lot at the state park.