You can always try Vaultek's Slider and mount it to the passenger seat. I usually just leave it on though.
Last year going to the NRA show in Indy, we stopped at a populated Cracker Barrel and 5 minutes before we left, some car pulled up and broke the window of my buddy's truck and stole all our stuff. They probably thought they hit gold when they saw my small gun travel safe, only for it to be empty because it was on me lol... Sucked losing some stuff that was priceless to me.