the problem comes in when you have a breakdown or even worse, an accident, the car gets hauled off somewhere, and someone calls the cops saying "i found this case that looks like it has guns in it...."
Doesn't happen. Tow companies generally mind their own business. Hell when I wrecked my 2009 camry on rte 2 the tow guy just towed it, done. I came back a day later and took the toolcase out of the trunk, which had a couple of loaded 40 round AK mags I had stashed in it for some
reason.
Unless your stuff is sprayed out all over the road it's a non issue, and in that case, you have bigger things to worry about (probably survival) than frilly shit like FOPA compliance.
In a typical break-down case, if you're really paranoid, just pay to get the guy to tow you out of the hot zone. Done.
-Mike