HvH,
These might help you out...they show the interior turret basket looking towards the right side. You can see the commander's seat as well as the gunner's and the base of the tread plate.
In this shot, you can see a cut-away diagram showing how the turret and basket fit into the hull.
Both of these come from Spielberger's Pz IV and Variants and are for discussion purposes only. You can clearly see that below the turret ring the entire "basket" is open all around although under the gun portion of the turret there are elements of equipment that are between the basket and the front compartment for the driver/radio operator. HTH