The Closure Plate Sub-Plate (CPSP), which defines the border between ex-vessel and in-vessel components of the Electron Cyclotron Upper Launcher (EC UL), bundles the waveguides into a sub-assembly which can be manipulated separately from the UL Port Plug (PP). The primary CPSP functions are to provide transmission line feedthroughs, support and alignment of the attached waveguides, neutron and gamma shielding, and Tritium/vacuum containment. The double CPSP concept, which is divided into In-vessel Waveguides CPSP and Thermal Isolation CPSP, was recently introduced in order to minimize the openings that expose the interior of the plug, to avoid the near environment activation in case of maintenance or intervention on the in-vessel components. This paper reports the most recent status of the CPSP as well as the analyses carried out to validate the design for normal operation. The fluid-dynamic analyses show that the power dissipated due to mm-wave transmission can be properly removed with an acceptable mass flow producing admissible values of pressure drop and temperature rise in the cooling systems. The results obtained in the thermo-mechanical simulation, validated using the ASME code, shows that the CPSP design is capable of withstanding the expected loads taking place during normal operation.