Drop Shadow Along Perimeter of Grouped Objects

Is there a way to add a drop shadow with a very tight gradient along grouped objects as a whole? Failing that, is there a way to drop a 3D effect in there to make the armored plating look 3D by making it appear "thick?" I'm not really getting the results I want with drop shadow, and these plates are in rings overlapping each other. Any suggestions would be appreciated. The effect below would work if there was a way to connect the corner nodes so it doesn't just look like a sloppy duplication.