If you're going with pykrete, you might think about freezing it in blocks and storing them in an ice house. Just bring out as you need and place in a normal cooler. That way you would have more choice as to where/when you use it and it might last longer into the warm season. If you were to construct the cooler from only pykrete, I would worry about the thing getting misshapen as it would melt faster in some places vs others. Plus there is the problem of fishing beers out of the sawdust/melt water mixture.