I got a keyed gunsafe (shoe box sized), used a motorcycle chain (thick bike chain) and some hardware to attach to the car on the floor of the backseat. It's THICK to where no normal bolt cutters will get through it. I leave it open with a key inside, so when I need to, I put my gun in it, and take the key with me. Only really use it when I go to the range, and don't go straight home after, I don't carry all those guns on me.
It simply looks like I've got a toybox, or toolbox in the backseat. If you bother to look hard enough to see it through the tinted windows in the back.