Tamiya PzKpfw IV Ausf D - Hull questions

Greetings!
i continue to enjoy the construction of this kit, but as i progress,
i notice that the hull is much like a block of swiss cheese!
i have filled the three holes in the bottom, and am working on the two rectangular holes on the sides (center, between roadwheels and idler or return wheels).
i have also filled some voids where the drive sprocket mounting piece 'keyholes into the hull, coming up short of the top.

all great fun, i assure you.

BUT - while dryfitting the upper hull to the lower last night
(while trying to convince myself that it would clear the smaller muffler that piggybacks on the larger one. - it won't, of course, but that is a problem for another day)
i discovered that w' the upper and lower halves joined, there is a large 'hole' on each side (left & right) of the upper hull that is not filled by the lower hull (which is mostly rectangular). it would let you look under the fender right up into the turret!

i reviewed the instructions and the remaining pieces, but i see nothing that would go in there. now, the various small holes in the hull (5, i think) are leftover from this kit's motorized days, i guess. but what purpose do these large open spaces serve?

i admit they are only visible if the tank is on it's back
(where it belongs, right, Sherm?)
but it is going to bother me. possibly a lot.

i intendt to cut styrene sheet to fill this space.
but before i started, i was wondering abt what any of you have done w/ this kit, or a similar situation.

if my description does not make sense, i can post a picture of it, i think.

thanks,
ed.