What he said.
I understand tanks interiors are not required but some tridimensional peepholes (the M113 APC had it ingame, if I recall correctly) for the driver and the commander are necessary to give you the idea you are inside of something. There is no need for ultra fancy stuff, I think a generic cockpit should do the trick and add to the realism/immersion.
The gunner should be fine with the traditional overlay/target-thingy though.