Plastic marine fuel tanks are not susceptible to corrosion and are less expensive and more durable than metal tanks. However, they don't have fuel baffles typically, allow fuel smell and may not be available in some sizes needed for certain applications. The increasing use of ethanol in gasoline, which can degrade metal tanks, has contributed to a rise in the popularity of plastic units.
Water in the environment and additives in the fuel can cause corrosion on metal tanks that leads to tank failure. A properly installed aluminum tank is typically rated by the U.S. Coast Guard to last about 12 years. Most plastic tanks are made from high-density polyethylene that does not corrode and lasts far longer than metal. Plastic tanks, which are machine-spun, use less expensive materials than metal tanks, so they usually cost less.
Many plastic tank designs do not incorporate baffles inside the tank, allowing the fuel to slosh back and forth unabated. The excess motion can increase the stress on the sides of the tank and cause structural problems. Plastic tanks may allow some fuel seepage resulting in excess fuel fumes. Most plastic fuel tanks are made in stock sizes that may not fit every boat, but some manufacturers offer custom plastic tanks built to the customer's specifications and up to 350 gallons in size.