I'm still not convinced it'd be of much help. The scenario I have in mind is the "late evacuation".
I have a similar gut feeling about the idea. Does anyone have any idea if most of the people running out of gas along the highways fleeing Katrina ran out of gas because the gas stations were closed/out of gas, or did they run out of gas because they were stuck in traffic and couldn't get to a gas station in time? Probaby both happened, but I'm curious if one reason predominated.
If it's the latter reason, then the storage facility idea may not turn out to be much help if you can't even get to it because the roads are so completely jammed with traffic that you can't even move. In this case, it's better to carry extra gas with you during the evacuation.
On the other hand, your idea makes more sense if the unavailability of gas along your route is your main concern--either gas stations for mile after mile are out of gas, or else the lines are so long that either it'll be out of gas or the hurricane will arrive, by the time you make it to the pumps. If the storage facility is still within the evacuation zone, then being able to get that extra bit of gas to drive to safety could be a lifesaver.