Is this the two door with the offset evaporator/condenser on one end? If so, the evaporator drain is either plugged or you are getting condensation from high humidity from when you open the doors.. Do you have sliding or swing doors? The evaporator drain just drop’s into a pan above the compressor. They tend to rust out and leak on the floor outside the cooler.
The only other possibility is that you coil has iced up and the fan air is carrying water over to the case.