In this study, the third and final prototype of a mobile micro-environmental calibration chamber for wall-mounted temperature and humidity transmitters was developed and validated. Building upon the shortcomings identified in the previous prototypes, the final design integrates advanced thermal management, optimized airflow control, enhanced humidification, and a high-accuracy sensor suite to achieve improved stability and precision. The chamber is compact, energy-efficient, and capable of generating and maintaining a controlled environment with high temperature and humidity accuracy. The device enables multi-point calibration directly on-site without the need to dismantle transmitters from the environmental monitoring system, significantly reducing downtime, operational complexity, and uncertainty associated with traditional calibration methods. Validation experiments demonstrated stable and repeatable environmental conditions across a wide range of temperature and humidity setpoints. This prototype represents a substantial advancement toward establishing a standardized, portable, and traceable method for the calibration of environmental monitoring sensors in regulated industries, thereby enhancing compliance with quality and regulatory requirements.