yeah you need both exhaust and inner movement.
you can accomplish both at once with an active exhaust and an intake that is at the furthest possible point in the box from the exhaust, like exhaust at the highest corner and intake at the lowest corner on the other side. the 4"duct booster fans at home depot are the right size for a cabinet grow, do active intake AND exhaust and you will be fine, and you can still run a very small fan inside the box if you want.

and no tin foil!