My computer screen isn't showing the shadow on the door you mentioned but I agree that would not have been an FS truck. If the triangle is upside down, then it could more likely have been a Bureau of Land Management vehicle.
I feel ya. It's hard to walk into an auto parts store and expect the kids to understand anything. Nothing torques me out more than asking a question and watching them start googling something I was hoping for a professional opinion on. Oh the kids today. Then again, that's what they said...