Both 40' and 20' containers are suitable with different door opening locations, rear and side.
Connecting a hot air dryer to a container couldn't be simpler by cutting circular holes for the hot air to enter the container above the dryer. A large rectangular hole at the bottom to duct the cooled air back through the dryer creates the option of recirculation.
Add an exit for the hot heated water-laden air at the far end, and you have a drier.
20ft container with rear opening doors with twenty standard steel stilages stacked inside.
20ft container with rear opening doors with eight standard potato boxes (6 x 4ft) stacked inside.
20ft container with side opening doors with eight standard potato boxes (6 x 4ft) stacked inside.
20ft container with side opening doors with twenty standard steel stilages stacked inside.
The diagram below shows the configuration of a basic dryer system, with access to the dryer chamber from either front or side.