The acoustic trim components play an important role in NVH designs for reducing the structure borne noise transmission and participate to the acoustic absorption inside the car. Over these past years, the interest for numerical solutions to predict the noise transmission through trim packages has grown, leading to the development of CAE tools focused on trim modelling. The finite element based methods are preferred for studying the low and medium frequency ranges. Their strength relies on the accurate representation of multiphysic interactions between the car structure, the trim (including highly dissipative mechanisms) and the car cavity. The incrementally restrictive weight and space constraints force today CAE engineers to seek for optimized trim package definition for reducing noise transmission. This paper presents a two step procedure which targets a reduction of the noise transmission thought the car body floor using a coupled simulation with MSC NASTRAN and Actran. The material properties of porous material, thickness of visco-elastic patch, embossment of supporting steel structure and heavy layer thickness are the design variables of the optimization process. The bead and embossment of the metallic floor structure is first performed using SOL200 topography optimization while considering a reference trim configuration (nominal values of the material properties). Once the optimum embossment pattern is found, the optimization of the visco-elastic patches properties and the trim package is started as a second step with Actran and the embedded NLOPT algorithm. The case studied consists in a complete car model including a realistic random excitation and a complex modal tire model representing the road irregularities. The study demonstrates that the trim package cannot be neglected during the optimization process. The floor bead and embossments have a minor impact on the acoustic response in the car cavity, conversely to the properties of the trim package. For a fixed car model including structure and cavity, which is generally already available by industrials, the trim modelling and the optimization can therefore fully be performed with the Actran for trimmed body tool.