The area behind the dive planes is discussed on the behind the hull casing thread.
http://models.rokket.biz/index.php?topic=233.0I have a picture of the Cod in that thread showing air canisters against the hull and centered is the gearing for the dive plane movement it's self.
The front area is a bit more difficult on seeing what's in there, I'm actually researching it right now.
The close ups of the Cod in current state shows coverings over holes on the bottom plate that at one time where probably open for free flood in the area.
As far as I can tell the top should have openings as well to the bow buoyancy tank.
There will also be framing in there.
Behind that area is the bulkhead to the chain locker.
Here's a couple pix of the Growler after a collision with a Jap ship.
And a Tench in the process of Guppy conversion.
I have the Eduard set as well but may modify or just not use that part since it doesn't seem to match the EB boats to what is seen.
If you will notice the pic above, you will need to modify or replace the torpedo shutters to be correct to the Cod.
Eric...