How big is the tube tent, that you can carry it around with you all the time? I can see stuffing a space blanket in my inside suit pocket, I carry at least two of them in my car (I also have a number of plastic tarpaulins). Mountain Equipment Co-op sells an emergency bivy bag made of space blanket material that would probably stuff inside a wool tuque or watch cap; is your tube tent about that size? I personally couldn't see carrying anything larger than that.