EPA web site says nothing about any specific volume for long term gasoline storage.
Use Proper Containers Use only containers approved by a nationally recognized testing lab, such as Underwriters Laboratories (UL). Containers should be fitted with a spout to allow pouring without spilling and to minimize the generation of vapors. Always open and use gasoline containers in a well-ventilated area away from children and animals.
Fill Cautiously Fuel equipment on a hard surface such as concrete or asphalt and use a funnel and/or spout to prevent spilling or splashing when fueling lawn and recreational equipment and always fuel outside where there is adequate ventilation to disperse the vapors
Store Carefully Store as little gasoline as possible and be certain to keep your gasoline container properly sealed. Store the gasoline in a cool, dry place and never in direct sunlight. Store at ground level to minimize the danger of falling and spilling. Do not store gasoline in a car trunk. There is a threat of explosion from heat and impact. Do not store gasoline in your basement.
Avoid Spills Avoid spilling gasoline on the ground, especially near wells. If a small spill occurs use kitty litter, saw dust or an absorbent towel to soak up the spill, then dispose of it properly Dispose Properly Do not dispose of gasoline down the drain, into surface water, onto the ground, or in the trash. You should check with your town concerning using your local household hazardous waste collection for safe disposal of excess or old gasoline.