In the healthy Miami-Dade County industrial real estate market rife with transactions, the $18.8 million sale of a cold storage warehouse might not seem notable. But wait until you hear more about the facility. The indoor space at the 231,686-square-foot warehouse at 18770 NE Sixth Ave. in North Miami-Dade has been kept frozen for the past 40 years, including during and immediately after hurricanes. “It is a unique thing,” said Dan McCawley, one of the attorneys…