I am looking for a liquid that I will use in the testing of packages
the contain liquids.  The basis for the inquirey is the regulations
for testing packagings for hazardous materials allows the
certification of upto 1.2 SG without increasing the drop hight.  If I
find a liquid of 1.2,  I can certify, and mark the pack EXACTLY as it
was tested.  The requirements are:
1) It is heavier than water, hopefully a specific gravity of 1.2 or higher.  
2) It must remain in liquid form at 0* F.  
3) It must be non-toxic - otherwise, Id just test the actual products.   
4) It must also be able to be stored for long periods (30+ days) at
110*F. without breaking down.
5) I will need a large volume (maybe upwayds of 350 gallons) of the
liquid, so I prefer it to be relatively economical as well.

I'm thinking salt water.

It was my understanding that salt water may or may not freeze around
zero.  Our chamber cycles betweem roughlt -5*F and up (defrost cycle).

Oops, my bad-- I didn't notice you said Fahrenheit.