Anyone have a source or lead for getting the locking gas cap. OR is this actually an issue of concern to you (the general and plural community YOU)?
I have a feeling that this large vehicle with the large tank may be an attractive target. I'm not sure if there's any anti-theft device down the filler neck.

 

There is a check ball at the bottom of the hose near the tank that prevent spillage in case of a roll-over. I have never siphoned gas so I don't know if anyone would be able to get passed it with a hose.
Any local jobber or autozone-type store should carry a cap for you.

 

depends on the year and options i looked on o'reilly auto part's web site they have them .