Chops,
There are several reasons why I or others might want to lock our gas doors.
1. Although siphoning gas may not be the biggest reason, it can be done without much difficulty! I have a small commercial siphon pump that I use on a regular basis to take gas out of my 2001 and now my 2003 Sport Trac to use in my lawnmower, and I have had absolutely no difficulty doing so. So what ever makes you think the Sport Trac has an anti-siphon gas tank, does not appear to work.
2. Some people and kids may wish to contaminate your fuel with something that could damage your fuel system.
3. Even small neighborhood children may find the fuel door interesting to play with and end up breaking it or, remove the cap and shove toys, sticks, or rocks in your fuel tank.
As you stated, the fuel door is just plastic and could be easily pried open if locked. Most vandalizm and thefts are crimes of opportunity. If they find your gas door locked, they will in most cases simply move on the next vehicle. If they are willing to risk getting caught by spending the time and effort to pry open you gas door, they probably know you and are not interested in vandalizing someone elses vehicle.
Yes, most American vehicles do not come with locking gas caps or locking gas doors, but most Japanese vehicles do have key or cable operated gas door locks.
wwashing,
My lock desgn has a hidden emergency cable that can be used to unlock the gas door if there were a failure of the actuator or wiring.
Darin,
The reason for making it electrical is that the door locks and unlocks without any conscience effort by the driver. Stringing the wires is simple and the door lock actuator has a simple lock/unlock mechanism built in. If you only use a cable, you will need to add additional mechanical parts like springs and levers to ensure that the gas door lock always returns to the locked position. And depending upon the locking mechanism, do you need to remember to lock the door after it is closed, or will the door automatically lock when the door is closed??
The simple cable release involves much more complex mechanical parts than using a simple door lock actuator that are typically available for about $5-$15.
...Rich