Most of the recycled shipping containers are at least 10 years old and have been on the ocean for most of their life. They have survived some very harsh conditions and are still in a sound solid condition, therefore as long as you keep the property maintained there is no reason why it will not last a minimum of 15 – 20 years. Also unlike a normal home container homes are earthquake proof and do not crack due to subsidence.
With this in mind, as with any home a container home does require some maintenance. A lot will depend on the location you actually install you home and the materials you use.
If you have treated the rust properly and used a good quality primer and paint then there should be no additonal painting needed for several years. If you find any damaged areas or spots where paint is missing then these should be treated as soon as possible to keep the container in good condition.
If you have used wood for exterior areas then as normal you will need to varnish and keep the wood treated.