Ron if you want to leave your gun in your car in a non Federal parking lot - do it however you want. Tuck it under the seat, stick it in the glove box, lock it in a portable safe welded to a seat, however you want. as there is no restriction to a non prohibited possessor over the age of 21 to carry a lawfully possessed firearm out in the open air public. I would highly recommend you do NOT unload it - the loading and unloading cycle in a restricted movement space like your vehicle adds an unnecessary chance of negligent discharge. Leave it loaded, remember to be extra careful of finger off the trigger while moving in tight quarters. A paddle holster for this easy on/easy off would be handy, if you plan on doing this a lot. I personally don't patronize places that restrict my lawful carry. Let the Chicago ex-pats and Calirefugees go there.