I. Case Background: Sewage Treatment Challenges under High Rainfall Load in Foshan During the Rainy Season In 2024, the Urban Management Bureau of a district in Foshan City, Guangdong Province, completed a procurement batch of sanitation vehicles prior to the flood season—including National VI Dongfeng sewage treatment vehicles with a 3308 mm wheelbase. These vehicles are primarily deployed for rapid pumping and treatment of accumulated rainwater and sewage in low-lying urban areas following summer downbursts. In accordance with local government procurement practices, the budget was capped at approximately RMB 393,000 per unit; ultimately, two sewage treatment vehicles supplied by Chengli Special Purpose Vehicle Co., Ltd. were delivered. These vehicles have now operated continuously for over six months in Foshan’s hot, humid, and rainy environment, successfully completing multiple emergency rainfall response missions—the durability of their anti-corrosion coating and sealing components has become a key focus for the client. Foshan is located in South China and features a subtropical monsoon climate, with an average annual rainfall exceeding 1,600 mm and high temperature–humidity conditions during summer—posing severe challenges to the chassis, superstructure, and electrical systems of special-purpose vehicles. Conventional models operating in similar environments often suffer from paint blistering, aging of rubber seals, and corrosion of electrical connectors. To address these issues, Chengli’s solution employs a dual anti-corrosion coating system—hot-dip galvanizing plus polyurethane topcoat—on the Dongfeng 3308 mm wheelbase chassis. Additionally, epoxy resin sealing technology is applied at critical locations such as sewage tanks and pipe joints, significantly enhancing environmental resistance at the material level. II. Key Equipment: National VI Dongfeng 3308 mm Wheelbase Sewage Treatment Vehicle The vehicle model delivered in this project is CLW5070GSSD6 (referencing official announcement parameters), built on a Dongfeng chassis with a 3308 mm wheelbase and compliant with National VI emission standards. Its core functions include sewage suction, solid–liquid separation, sewage transfer, and preliminary purification. During Foshan’s rainy season operations, this vehicle undertakes the following primary tasks: • Floodwater Extraction: Utilizes a high-capacity vacuum pump to rapidly extract standing water from low-lying road sections—each operation covers approximately 3–5 work sites. • Sludge Removal: Employs a rotatable suction arm to clear sedimented sludge from storm drains and drainage ditches, preventing blockages. • Emergency Support: Functions as a mobile sewage treatment unit during heavy rainfall events, performing rapid separation and treatment of sewage collected at temporary pumping stations. III. Core Performance: Sealing Component and Anti-Corrosion Performance under Hot–Humid Conditions Actual field feedback from a municipal sanitation department in Foshan highlights the exceptional durability of Chengli’s sewage treatment vehicle—particularly its sealing components and anti-corrosion coating. Specific performance data is as follows: 1. Sealing Component Durability After three consecutive months of intensive rainy-season operation, all rubber sealing components—including manhole covers, valves, and flanged pipe joints—showed no leakage or visible signs of aging. Testing confirmed that, under ambient conditions of 35°C temperature and 90% relative humidity, these seals maintained a sealing pressure of over 0.8 MPa—exceeding industry standards. 2. Anti-Corrosion Coating Performance After 180 days of outdoor parking and operational use, inspection revealed no coating delamination or rust spots on the vehicle body. Notably, the interior surface of the sewage tank features a glass-flake heavy-duty corrosion-resistant coating, offering acid–alkali resistance across a pH range of 2–12—effectively resisting ero