Should I Ground my Shipping Container
First of all if your container is sitting directly on the ground then there is limited risk of lightning strike, electrocution or damage to stored contents. But if you read my blog regularly you know that I would not recommend sitting a container on the ground. Basically a shipping container on the ground a) will dig in b) be hard to move and c) will rust quickly as it will not dry underneath.
So if you have your container sitting up on concrete, wood or tires: congratulations, that is sensible. Although it is probably a good idea to ground your container because there is a risk, albeit small, that under certain circumstances there could be a lightning strike.
Example: If you have a container up on wood let's say and you enter the Seacan during a thunder storm. In the unlikely event that you have one foot in the container and one foot on the ground as you enter or exit and this is simultaneous with a lightning strike the electricity will pass through YOU to ground. This could be fatal.
Wood and tires are conductors, but poor conductors. Wood can contain a lot of water and this improves the conductivity but a human body may be a better conductor and electricity will always choose the easiest root to earth and you really don't want to run the risk for the sake of a simple grounding kit. Also electricity flying around the container could well damage contents so for the sake of a copper grounding rod you might as well ground your container.
Grounding a Sea can
Simple grounding kits are available in farm supply stores. Basically you need a 3 foot copper grounding rod driven all the way into the ground and then the rod should be welded to the heavy chassis of the shipping container using a ground cable. The copper rod will be a better conductor than your wood, concrete blocks, tires or you.