Let's head off your rationalizations :
1. The brand is identified. These are tailor made to store biologically dangerous corpses and they were specifically manufactured for military clients. They're too expensive otherwise to acquire for any other purpose, being custom manufactured for this sole use.
2. That plastic will eventually degrade in sunlight irregardless of it's rating. Those are not being stored there as a convenience for anybody. They are there only temporarily.
3. Many, many people have pointed out that Atlanta is the airport hub of America and it would be expected to store these coffins here for shipment as quickly as possible to anywhere in the country.
U.S. Government Orders Half A Million Cheap Coffins. They're expecting a lot of sheeple to die soon.