Simple answer to the question.
1, First and foremost THE product should always be at the required temperature prior to loading the trailer.
2, If loading fresh produce always try to cover the top 4/6 pallets with cardboard or something similar.
3, If a load needs to be transported at Minus settings. IT must be pre chilled to that temperature PRIOR to loading as a reefer is not designed to freeze loads But maintain the load at its Loaded Temperature.
4, Soft fruit ( Strawberries / Raspberries etc ) should be pre- chilled then transported at + 32F