I seems that yall are coming around to the right answers.
1. A firearms dealer DOES NOT have to accompany you to your car when you purchase a firearm. That is FUD.
2. If you DO NOT have a firearms carry permit, then your purchase MUST be in a locked container while on public property. So if you put your purchase in a locked container, unloaded, it doesn't matter if there is a school zone outside the door.
3. For general purposes, a trunk is a locked container, but sometimes there is an issue getting from private property to you vehicle when in a school zone.
4. If you have a firearms carry permit or license, you are exempt from the federal law. The federal law does not specify whether that is a permit for open or concealed carry, so both are allowed.
5. CAVEAT: STATE law varies as to whether your CCW is valid ON School property. Some states, all handguns are banned irrespective of licensure, others allow it. And some states allow you to carry (with a license) if you have permission from the appropriate school officials. The federal law does not address the issue. EXAMPLE A: A California CCW permit allows concealed carry on school campuses. However, some sheriffs or city police chiefs (legally) impose conditions on the license banning school carry. EXAMPLE B: If I read the news correctly, Indiana recently passed a clarification to their law allowing carry with a license in school parking lots, but the license is still invalid for carry anywhere else on a school campus. So you can pick up the kids without locking up your gun, but you cannot attend the PTA or p[aren't/teacher meeting while armed.