The article investigates the structural behavior of closed monolithic rectangular tanks, constructed in a single technological process without interruptions or expansion joints, intended for application as floating platforms in inland waters. The research focuses on the assessment of their static performance under multiple load conditions, including hydrostatic pressure acting on the walls and bottom surfaces, as well as uniformly distributed loads applied to the upper plate. The structural analysis was conducted using the finite difference method formulated within an energy-based framework, assuming a Poisson’s ratio ν = 0. On this basis, computational results were obtained and presented in the form of diagrams that illustrate the variation of bending moments at characteristic locations of the tanks. The calculations were performed manually using custom-made spreadsheets. These diagrams provide insight into the load-bearing behavior of the system and allow identification of critical stress zones. Beyond the structural analysis, the study also includes verification of the buoyancy, overall stability, and metacentric height of a selected tank prototype fabricated for experimental evaluation. In this particular case, the influence of temperature variations and ice floe loads was additionally considered in order to simulate realistic operational conditions in inland water environments. The article concludes with photographic documentation of the pontoon prototype, demonstrating the practical implementation of the design. The results confirm that monolithic rectangular tanks exhibit favorable structural and hydrostatic characteristics, thereby validating their suitability as efficient and reliable structural units for floating platform applications.