Vinegar speeds up rusting because it contains a dilute form of acetic acid; positive hydrogen ions in the acid remove electrons from iron, ionizing it and making it susceptible to rust.
They have been designed to withstand the punishment of long distance ocean travel and to protect the goods inside of them during transport. Most often, shipping container floors are one inch marine plywood made from tropical hardwood such as Keruing or Apitong.
Storage containers are constructed with 12- or 14-gauge corrugated steel sides. Container frames are made of minimal 6-8-gauge steel. Containers have approximately 1" hard wood floors that are treated. Standard containers come equipped with a cargo door.