ive had gas taken from both of my toyotas now. both siphoned i believe. the truck i found the cap on the ground and didnt even realize it was mine. 
took bout 3/8 tank from that. got a locking gas cap after this. 
itll help at least, probably makem move onto the next rig insteada mine at least. which sucks for whoever else, but sorry.
those locking gas caps are a joke,
i used to have one, and when i lost the key to it, i discovered how easy they are to get around...
watch, take another key, or a small screwdriver, stick it in kinda hard, and then just play with applying pressure both ways and spinning it off, eventually youll get it to catch and it will spin right off, usually without even hurting the lock...
On another note, we have to keep our trucks and their tanks locked up tight. a 128 gallon tank on each side of a truck, at $5 a gallon is just too tempting to people, and too much of a loss for us to risk.
