I am going to building a storage "shed" that runs the length of my garage on the side of my house. Think of it as a 20 to 25 foot long by 3 foot deep storage shed. I would like to build an insulated portion of the shed for long term storage/aging of kegs and two barrels. I am in Portland, OR - not too cold, not too hot. How much insulation will I need? Any ideas on how to do this?