Temporary shelters, though designed for short-term use with lightweight materials, are often occupied for extended periods, especially in low-income regions. Despite their provisional nature, ensuring adequate thermal comfort in such structures over time is essential, but limited research exists on this topic. This chapter addresses this gap by presenting the results of an experimental campaign aimed at characterizing and evaluating the hygrothermal indoor environment of the HOMEDONE construction system, i.e., a modular, lightweight shelter constructed from 3D-reinforced EPS panels. Following a preliminary assessment of the in situ thermal transmittance of the panel and the airtightness of a modular experimental unit, the indoor hygrothermal climate was monitored through spring and summer. Findings indicated that low thermal transmittance of the panels and strong airtightness enhance the thermal performance of the system. Still, with closed openings, the indoor temperature and humidity can reach unacceptably high levels during warmer seasons due to the low thermal and moisture buffering capacities of the building elements. Long-term occupancy in hot climates remains challenging for HOMEDONE units, underscoring the need for improvement intervention to mitigate overheating and ensure thermal comfort.