Ideally, the container should be positioned on a concrete slab as above, but a good layer of hard standing such as '4" and dust' could also be ok. The container needs to be elevated on concrete blocks to allow a crawl space for connecting drainage pipes from sinks etc. The site also needs to be accessible by the lorry delivering the container, with the container itself being lifted off the lorry with a high reach crane bolted onto the back of the lorry. The container floors may not be well  braced, so extra piles of blocks should be placed anywhere that heavy equipment of tanks are going to be positioned internally.