No matter how well a container is designed some good judgment has to be made in how it is used particularly with flammable liquids. There is a reason that propane tanks can only be filled to 80% capacity. That is a good choice for any liquid container that will be exposed to temperature changes and in particular if any heat sources are involved. That is also the reason that the Vanagon fuel system has expansion tanks and why vehicle fillers are in the side of the tank so there is always some air space somewhere. As for venting, that is only a temporary fix when a heat source like sitting in the sun is applied. The vapor pressure will be determined by the liquid and its temperature. Since gasoline can make enough vapor to burn at ~-40 just imagine what it can do heated to 120+. Now let's take this container and place it so that that the sun can hit the large surface area of the side. This way we can heat it up even faster. If we vent enough the gasoline will be gone. Oh, and lets place this container outside and over our heads. Just a whole bunch of bad ideas.  

Dennis