I have the crossivers in my doors for about two years and have had no problems. They jsut have a metal strip glued to them and screwed into the door. The crossovers are probably not active which would mean electronics so they are just resistors and coils soldered on a board. I think it would be very hard to shake them hard enough to break them. It would keep them out of the way and make wiring simpler. Why don't you want to keep the amp on you back seat wouldn't the shelf hide it?