It's probably worth mentioning that even a weak mixture will provide burst protection but not freeze protection. I've seen where a weak mix slushed up in the radiator blocking the coolant flow thereby causing an overheat situation (it was too cold so the car overheated!). This is more of a problem here in Alaska than in most places. If the vehicle is not going to be driven but just stored outside in cold weather I would chose something closer to a 30% glycol mix. This makes for a bit better cooling in the summer compared to a 50/50 mix.
