I am thinking about building an interior room in my garage at the cabin that would be **** near impossible for someone to get into and am looking for ideas. This is a place that I would put my gun safe in plus use for long term food storage, etc. A metal door with a crossbar and a beefed up frame is a given but am wondering what to do about the walls. I am figuring 2 x 6 construction with sheetrock either side but am looking for something relatively cheap to fill the walls with. I am thinking of something that couldn't be kicked in or opened up with a chainsaw.