I don't know what you drive, but in most late model cars, the trunk usually has a little slot that keeps your spare tire tools in it, and its usually a pop-out part of the inside of your trunk thats pretty discreet...
Also, in the trunk, if your car has a spare tire, usually its kept underneath the floorboard of the trunk, and I don't think that the 5-0 would bother lifting it up and checking under there...
That might be a good spot...
And at the same time...if its in your trunk period, they're going to need a warrant to look in there, if its locked, and they didn't actually smell bud in the car, or what not.