“A student is dead after a firearm was accidentally discharged in a vehicle in the parking lot of Dalhart High School.
…
According to [Superintendent] Byrd, a student not enrolled in the district went to the high school at lunch and picked up three students when the firearm went off in the parking lot.”
Just don’t do it. Fooling around with guns in cars is a Serious Mistake that can easily lead to a tragedy.
If you have to put it in a lockbox, have a lockbox that’s big enough for the holstered gun and put the gun in the box without removing it from the holster.
tacticalprofessor 
Exactly this: “have a lockbox that’s big enough for the holstered gun and put the gun in the box without removing it from the holster.”
I am astounded by the amount of unnecessary handling of loaded, unholstered firearms. I have ruled out practically every single safe advertised on FB, Instagram, etc. precisely because they are too shallow to hold a holstered firearm. It is ridiculous to have to go through a relatively dangerous process (unholstering/reholstering) to move the firearm from a relatively safe condition to another relatively safe condition.