I am almost positive the rules haven't changed...
In Street 1-2 your installation can't prevent the normal operation of your seats being able to fold down/up, but you can compete with them in either up or down position.
In fact, if you bolted your box to your seatback so it flipped down with the seat and was closer to the front of the car, that would even still be legal as long as it didn't protrude past your front door sills!
