Make a room within itself. Have a air gap b/w the 2 walls. Make sure that that 2x4's don;t touch the new wall you make i front of the existing wall. Then put the foam used on the outside of house in b/w the new walls 2x4s, then cover wall with 1/4 playwood, then add 1 1/2in egg crate foam to it. That should do the trick.