Fuel tanks are designed to perform and withstand under sloshing forces, extreme event load cases and vapor pressure for the life of vehicle without any leak. Present design considers the design parameter to meet the structural strength of the fuel tank. The dimensional modifications, thickness variation and pre-stresses generated during manufacturing processes are not fully incorporated in design. This actually reduces the life of the fuel tanks than the intended life. Customizing or sophisticating the manufacturing process to obtained design intended part will increase the product cost which is not accordant with cost competitive automotive industry. This paper presents the improved design methodology to enhance the fatigue life of the fuel tanks by considering the manufacturing process potential. A detailed study has been made to understand the changes in the dimensions and profile of the sub- parts during manufacturing process. Residual stress and formability strain during stamping and rolling process has been analyzed in CAE through single step forming method using Altair hyperform. Spot weld fatigue analysis done with various gaps between shell and baffle, and varying nugget size in MSC Fatigue software. Statistical analysis was carried on the finished product dimensions to arrive at the optimum profile and dimensions to minimize the pre-stresses. The pre-stresses in the modified design were found to be comparatively lesser by 65% to the existing. The predicted life improvement was found to be significant. The modified design was manufactured and validated in rig, and found to have fatigue life around eight times better than existing.