The effect of salt mist exposure on the surface structure and permeability of thermoplastic polyurethane used in the production of temporary storage tanks and transportation of diesel fuel was investigated. After exposure to salt mist, the analysis of microphotographs showed the alignment of the surface of the polymer material. IR spectroscopy revealed a change in the chemical composition of thermoplastic polyurethane, and the appearance of a quaternary ammonium salt, which leads to an increase in the polarity of polymer macromolecules and increases the relaxation rate of the polymer material structure. An approach to modeling the natural loss of diesel fuel during storage in elastic tanks is proposed. The model parameters allowed us to quantify the effect of salt mist on the diffusion permeability of thermoplastic polyurethane for diesel fuel. At a storage temperature below 60 °C after exposure to salt mist, the tightness time increases and the natural loss of diesel fuel decreases during storage in the tank.