I don't think your strange at all for checking your back seat OR for going out so late! (I would too for smokes!)

My hubby lived in Las Vegas for 6 months a few years back and it took me quite a while to get used to being home alone at night. (Yes... even with Buddy & Sierra home with me! I'm such a baby!)
There were times that I would turn off all the lights in the house (so the boogie man outside couldn't see in ) and put Buddy on a leash and walk him around room to room. Then open the back door and have him check out the back yard too.
No body screws around near my house when Buddy's on guard!

Even with them in the house, I still find myself pulling the shower curtain back to take a peek once in a while.