As long as you have a carry permit from the state you're in, the GFSZ Act isn't going to be a problem for you, as long as you're in that state. Leave the state of NC on the other hand, and you have issues.
For example, to get from Boone, NC to Johnson City, TN, most folks would take US-321 and be over there in an hour and some change. However, there are three high schools less than 1000ft from that highway on the TN side. I'm sure there are hundred of offenders that pass through here every day that don't realize they're breaking federal law. Getting around this would require a 2 hour detour to Asheville to get to I-26, and take that to JC. But I'm not even sure if you don't pass within 1000ft of a school on I-26.
This just goes to show you how ridiculous the law is, and why it's never been enforced. Staying within the boundaries of the state your permit is issued is the exception to the rule.