Slippery slopes, fine lines, technicalities, hoops, and gray areas....
I guess we're a little off-topic, discussing school carry vs. faculty leaving pistol in car in parking lot. But while we're on it, I'm wishing Zigziggityzoo was here. He pointed out some interesting stuff when he and I last breeched this subject. He pretty much turned me off of OC on school property. Bummer, yeah. But this is the Readers' Digest version of what I got from our chat about it...
I'd asked that, if OCing on school property, WHO specifically has the authority to ask you to leave? And it goes something like this... the school's technically run by the school board, who delegates the authority to the superintendent, allowing him to delegate that authority to whomever he pleases. So if he's given that authority to the janitor or hall-monitor, they actually DO have the authority to have you leave the property. What it came down to is that essentially ANY employee of the school may have that authority and to be safe and cover your arse, you should leave upon being asked to by anyone since there's no solid way of knowing who's actually got that authority or not.
I thought thru the scenario and was thinking that if asked to leave by someone, say, a teacher, one might ask the teacher if he or she has the authority to do so. The most likely answer will be yes, whether true or not. If you leave, it's over. If you don't abide or call his or her bluff, they'll most likely place a call and you'll soon be explaining it to the badges. I mean, any way you look at it, it's hairy. I decided that even as much as I'd like to OC even on public school property, I'm not getting into that tangled SNAFU of a web....
Back OT - I think the verdict is that you're legally good to go, leaving gun in vehicle, less any prohibitions in employee policy.