Shipping containers are great for storing goods, the very reason they exist Is to house goods as they are carted across the planet, so they are ideal, theoretically. In Australia, shipping containers are very cheap and often used as an affordable "shed" for storing furniture, tools and other odds and ends.
The problem, however, is in the flooring. Whilst the majority of the container is lovely termite proof steel, the flooring usually is not. Marine ply or timber boards are generally used as flooring in shipping containers and seldom is it completely termite proof. Although termites may not eat out the flooring completely, the flooring provides little resistance to the, gaining entry to the container.
The environment is also very suitable, if the container is sitting close to the ground, is left undisturbed and it has little ventilation (most containers have minimal ventilation by default) then it's a perfect little home for them!
So, how do you protect a shipping container from termites?
Ensuring the container isn't touching the ground is your number 1 defence against termites getting into the container. Allowing plenty of air to flow freely under he container will reduce the moisture and reduce the chance of getting termites in the container.
Additionally, you should ensure that the container rests on a material that does not allow th termites to easily get in undetected. Steel posts are ideal.
Either way you should regularly check the contents of your container, especially looking underneath the container and keeping it clear, just in case some little friends decide to move in!