Keeping valuables in the vault

I just filled up my truck's gas tank, and I haven't had to spend that much since Hurricane Rita. One fillup for my truck, to top off the tank with 18.777 more gallons, was $58! Now I'm really glad I've got a locking gas cap, altho I'm surprised I haven't heard of cases of siphoning thieves yet. Instead all the gas thefts in the news are drive-offs from the stations.