The integration of modular container for Onshore Power Supply (OPS) systems for electric boats presents a strategic advancement in sustainable maritime infrastructures which are under-developed. This study explores the design and production of lightweight, modular containers made using composite sandwich panels with basalt fibre skins, extruded polystyrene (XPS) cores, and epoxy resin matrices. The sandwich panel production process uses one-shot vacuum infusion, ensuring uniform resin distribution and minimized void content. Basalt fibre, known for its high tensile strength, thermal stability, and resistance to corrosion, offers a sustainable alternative to conventional synthetic fibres. Combined with XPS, which contributes thermal insulation and low density, the resulting sandwich structure achieves an optimal balance between weight reduction and mechanical performance. These modular units are tailored to meet the general operational demands, providing adaptable, durable storage and systems housing. Experimental tests confirm the composites’ favourable strength-to-weight ratio and environmental resilience, highlighting their suitability for marine applications. Furthermore, the modularity supports scalability and ease of maintenance, aligning with the dynamic logistical needs of modern electric boat operations. This research underscores the potential of advanced composite manufacturing techniques in maritime applications, contributing to the broader objectives of energy efficiency, operational flexibility, and sustainable design in the naval sector.