I have blanked off the rhs sponson, and covered the floor with plastic card. I decided not to have it with a removable superstructure, because the gaps that would leave at the rear of the hull would be too big. The superstructure needs to be fixed to the hull to allow the join to be properly filled. I suppose I could superglue some plastic card to the rear plate, but with the rear hatch open, and the superstructure hatches open, the interior will be sufficiently visible (and hopefully not too tacky).
Edit: (pics added)
I used a grinding wheel in a motor tool to remove the excess hull wall that remained above the pannier /sponson. When I did this task on the left hand side, I used a slitter, which was much quicker.
This shows how bare the interior is, even after I'd added a length of milliputty "breech". Note the squared-off edges of the gun mounting casting representation.
The following picture shows how much could be seen from the outside through the open hatches, without even getting very close!
The next step was to make the gun mounting casting a little more life-like. So, I used the grinding wheel that was still in the motor tool to round off the edges ...
(you can compare the appearance of the "before" and the "after" with these two photos)
... then I spread some Squadron Green Putty over all the surfaces, and rubbed it with my fingertip until it dried, leaving a sandy, cast texture...
I still have a little bit to add to this, above the gun barrel. You will note that I've removed the inaccurate MG34 mounting, together with the m.g. I also rounded off the square edges of the kit barrel with a router bit in the motor tool.
Next, I thought about how I was going to represent the transmission and brakes. I decided to use a styrofoam food tray, cut into discs with a circle cutter, to save my precious plastic card for more important things.
As this food tray had an intrinsic subtle texture, I also cut out a rectangle of it and used it for the floor on the driver's side.
The drive shaft is a piece of sprue from the 1:72 Hasegawa Ostwind kit, sanded to a regular circular section by securing it in the chuck of the motor tool and spinning it at 2000rpm against a piece of sandpaper on a sanding block. Despite the optical illusion of the picture above, it is straight!