dry ice and beer storage

hi,

sorry i didn't add this to the other dry ice thread, but i'm new and couldn't find out how to post to an old thread. anyway, i am going to a music festival for 4-5 days and i need a way to make ice last as long as possible. i'm going to have lots of beer that i need to keep cold and i'll be opening the cooler pretty frequently. i'm not planning on being able to make runs to get ice once i'm there. i've got a very large (i think 150qt) cooler. i've read about wrapping dry ice in foil and newspapers and putting it on the bottom of the cooler and topping it with wet ice. i've also read about putting dry ice in a small styrofoam cooler and putting that inside the large cooler, and filling the rest with wet ice. i'm only going to be putting as much beer as i need in the cooler at one time, and i won't leave beer in overnight. so my question is, do you think either of these methods would do what i need? if the beer is rotated regularly and quickly can i do this safely without the beer freezing? do i need to worry about pressure building up within the cooler when it's closed from the dry ice? how much dry ice will i need? i'm not so much worried about the cost, having ice consistently for 4-5 days is what's important. any advice you can give me is greatly appreciated. thanks in advance!

matt