Each recently built shipping container is designed to take the weight of 8 loaded containers on top of it. Each container can weigh, when loaded 30.5 tons gross weight each, which = 244 tons on the bottom container. This load is supported by the containers four corner posts.
At the top and bottom of these four corner posts are the corner castings.
Four in the top of each corner and four in the bottom of each corner. And it’s on these bottom castings your container should sit, If your ground surface is not entirely flat you can level the container by using four independent plinths, such as concrete blocks, bricks, wooden blocks etc., but they are most successful when placed upon two wooden or concrete railway sleepers or similar, placed transversally one each end.
This helps maintain the ends of the container in a square configuration. Keeping the container square is essential for easy opening of the doors and also keeps the door seals tight to the frame to prevent water ingressing.
The container floor is usually 28mm thick laminated plywood which at manufacture used to be fully covered with bitumen preventing moisture ingress that is not always the case nowadays and by raising the containers off the ground this creates an air flow under the container, which keeps the container floor dry and the steel understructure rust free.
Placing a packer under the castings at the front (blank end) of the container will, if there are any leaks or spills send the fluid to the rear entrance where it will be noticed, whereas if it remains at the front or centre it will puddle unnoticed and cause you a lot of damp and condensation problems before you noticed anything.
If your container is to stay in position for a lengthy period and you have concerns about vermin, before you position the container, place a mat of chicken wire across the area of the container footprint and cover with pea shingle.