----To do so, will invite a complete split and breakage at 20-25 degrees. This is plastic and you would be better off using clear water out of the tap for defrost. Using a chemical agent will eat into the acrylic top material after a couple of years and it is "no good" for rubber either. ---A preferred method of an instant garage would be to put a Z3 Solutions Tyvek Cover over it....they ar sponsors on this message board. Good Luck!!!!! I live in Boston, and have no garage. My Z3 survived the winter outside without trouble. The main problem is removing ice from the plastic rear window, because an ice scraper would gouge the plastic. One solution is to hit the window from the inside to knock off the ice. An even better solution is to turn on the heat to melt off the ice. Another possibility would be to get the removable hard top, which has a glass rear window and electric defroster. This is a ~$2K option.