To stop mould growth the easiest method is to control moisture levels or ideally remove the moisture all together which can be very hard when it comes to shipping & sea freight. There are a few methods to consider depending on your cargo and shipping options / capabilities.
Desiccants
Using a desiccant is the most common method and involves placing a desiccant material in the sealed shipping container. Desiccants are materials which in their natural state absorb moisture. These materials are dried out before use and once in place they absorb moisture from the air. You would have seen a form of desiccant each time you buy a pair of shoes and they come with a silica gel packet. However you must ensure you have enough desiccants for the volume of your container and the time it is sealed for as once desiccant reach their full capacity they will begin releasing this moisture back in to the enclosed environment.
Dehumidifiers
A dehumidifier is a purpose built electric appliance which lowers humidity by extracting water from the surrounding environment and draining the water away. These appliance do require a power source however they are proven to be more effective than a desiccant, especially in long term shipping. Dehumidifiers will also remove excess moisture from wet materials like timber pallets and crates.
Ventilation
Ventilation is a limited option depending of the exposure of your shipping & sea freight to external elements. The purpose is to allow any excess humidity and high temperatures to regulate with the outdoors however if you crates are shipped externally (on the deck of the ship) then this may not be a suitable option.