Th concept is interesting but I believe also very dangerous. The air we exhale is only about 4% CO2 (I think lol) Dry ice is 100% CO2 and the volume it gives off as a gas is tremendous compared to its solid state. Now a well ventilated slow release may be fine but I wouldn't want to find out the hard way. A big block of regular ice seems the way to go.
Got it, no dry ice, just regular Ice. thanks for the replies all. I am going camping this weekend and my give this a shot.