[arbezc]

Thanks Marwil, I found a clear image on-line that confirms what you say. The rear half appears to protrude downwards about 1/2 the extent of the front section of the tunnel.

Does anyone know what the purpose of the 12 or so 2" round forms are for? I would guess drains holes used in manufacturing? Mine are sealed on both sides with sound deadening & undercoating.