Before you build your foundation, do a layout of the area surrounding your new home. The septic tank will need to be as close to the bathroom as possible and accessible for future maintenance. The electricity will be entering the container from a high point, usually in the kitchen close to the internal fuse box. The water will have one entry point, usually from your water tank on the roof, which would be below your rainwater catchment system. It is very important to take your time with the foundation so the containers will sit perfect and level during instalation. Double Check all the measurements and work with the proper equipment. If you are planning to stack containers then you will need to re-inforce your foundation. This would usually include an additional cement cylinder in the center.
These are the things we do regarding the foundation here in Costa Rica.
1. Know the position of the septic, electricity and water connections.
2. Decide on cement canisters, wood beams, metal jack stands or used tires.
3. Weight requirements and structural engineering. This means an extra canister of cement per large cut out.