It is actually quite hard to create gasoline explosions in closed containers, unless you are in a mighty frigid climate in the winter. You will generally have to have some sort of event that would introduce gobs of air to some portion of the vapor space (where an ignition source exists) and make it go below the UFL. Certainly not impossible, but you want to consider what is this aeration mechanism, in addition to pondering the ignition source.

On a related topic, Dr. Lori Hasselbring has a paper in the program for Fire & Materials 2007 conference on the topic of explosions in plastic jerry cans. These are somewhat less hard to get below the UFL.