Questions about buildings without foundations

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I am using EnergyPlus to simulate a structure made from modified shipping containers. This structure has no foundation, which distinguishes it from typical buildings. It consists simply of shipping containers placed on the ground with interior insulation installed. In this case, is it appropriate to use Kiva for calculating ground heat conduction? Or would it be acceptable to use Ground Surface Temperature? Note that I do not have data on the ground temperature at the building surface. Undisturbed ground temperature data can be obtained from EPW files.