We shipped out over 20 boxes yesterday and every box got a heat pack, it was 82 yesterday where we shipped from. The box will arrive in NC in the middle of the night and arrive to its owner by 10:30am. Therefore, the package will be at the airport, UPS and in the back of a UPS truck which all may take around 8 hours. Therefore, your coral will be in temps of 50 degrees or below for nearly half of the time. Unless you are using a 2 or 3 inch thick styro box then I would highly suggest that you put a heat pack in the box. Even if you put a 12 hour heat pack from ***** sporting goods or something like that.
Just passing on my experience and what I would do. Yes the coral may arrive alive without a heat pack but shipping in cold water can take days to take its toll.
On the other hand, do what YOU feel is right because you are the one that is shipping the coral.