But even in Chicago, why would a cop look in your trunk?
I know this is far from a novel statement, but as frequently posted and stated on this board and elsewhere, you DO NOT have to consent to a search of your vehicle. Barring exceptional circumstances (probable cause to believe you are committing a crime; vehicle is in a horrible accident and rescue workers have to cut it open every which way; etc.) there will not be a valid reason for a Law Enforcement Officer to look in an area of the vehicle not in plain sight.
If you are in a car with a trunk, keep the firearms and ammo and accessories in the trunk, and don't give the police an excuse to perform a search. In other vehicles, in a nondescript, locked case, covered with a tarp, you're not giving them cause to believe you have "contraband". If they ask to search, or "just take a glance in the trunk", or "open the door so I can check something", just say "no". Politely, but firmly.
If they take posession of your keys involuntarily, or open or enter your vehicle without your permission, make it verbally clear that you don't give permission for them to do so, but don't interpose yourself physically. Verbal denial of permission is enough to preserve your fourth ammendment rights (as interpreted, anyway), while physically blocking or restraining an officer who is performing the perceived duties of his office will land you in all sorts of doo-doo. (Also, it's still wise to do the whole 'unloaded in a locked container, with ammo in a separate container' thing whenever in doubt about local or state laws, just in case an exceptional circumstance occurs, and the police have a legit reason to be in your trunk.)
-twency
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And now you know. And knowing is half the battle.