It is good to be cautious but no need to be freaked out. If the gas is in a proper container in good condition and there is ventilation at the bottom of your box your not likely to have issues. The big concerns are during refueling particularly with a hot engine, spills, and static electricity. Sheds and garages all over the country would be exploding and raining down parts of gas cans, lawn mowers, weed eaters and blowers if just storing gas were such a conflagration danger. Be wary and don't let it bite you in the ass but no need to be paranoid.