that is going to be a stupid law to enforce. what exactly qualifies as a hidden compartment?
my old car was a 2002 Toyota corolla, about as vanilla a car as one could possibly have. it had secret compartments in the trunk, you had to lift the carpet, then a board that looked like the trunk floor, then a hidden side flap to get to the car jack, and there was an empty one on the other side i kept an air compressor and jumper cables. These were completely hidden compartments.
what about people that buy used cars? how is one guaranteed there aren't any compartments they don't know about. technically you start pulling the side door panels and dash panels off and there are "compartments" under those, and many of them snap on and off, any void could be considered a hidden compartment, and cars are full of them.
having hiding places isn't illegal. having illegal stuff is illegal whether or not you hide it.
what's next? can we arrest anyone crossing the border who has a butthole just because one could potentially hide stuff up it? christ what a hideyhole...