New generation Launch Vehicle uses different cryogenic propellants like liquid hydrogen, liquid oxygen and liquid methane stored in propellant tanks. The heatin-leak to the propellant tanks adversely affects the quality of propellants. It leads to underutilization of stored quantity and early cavitation of pump. The insulation of the tanks prevents the major portion of heat-in-leak, but the heat transferred through structural mountings to the tank is also equally important. The mountings can be insulated, but there will be heat transfer from structure through metallic conduction. The computation of heat-inleak through a non-uniform mounting bracket is difficult on account of the complex three-dimensional heat transfer through the bracket and the difficulty in estimating the thermal contact conductance across the joint. This paper presents the theoretical thermal model to estimate the heat-in-leak. An experiment is carried out simulating the structural mounting with temperature gradient by servicing liquid nitrogen. Based on the experiment the thermal contact conductance used in model is fine-tuned. The heat transfer is also verified using the rate of boil off liquid nitrogen in the vessel. The temperature across the mounting stabilizes 3600 s after servicing liquid nitrogen. The experiment revels the axial heat flow and the heat leak through the mounting is of the order of 121 W. The adequacy of the proposed insulation configuration is also verified experimentally.