Triumph TR4-250 Scuttle Vent Lid
Closing the vent lid when the car is not in use will stop a lot of both water and debris from getting into the plenum. There is another advantage to be gained from keeping the plenum area of the bulkhead clear. First time out in hot weather, you turn on the heater fan to cool the car interior. Don't you just hate the ticking of the fan, closely followed by the fascia air vents spitting forth at the face level a potpourri of chopped leaves and insect bodies!