If memory serves, the 'gunner seat' is just basically standing next to the big recoilless rifle we've got mounted on a swivel. So your head would be poking out the top of the APC and you'd have a 360 degree view. 

[img]https://img-new.cgtrader.com/items/13520/large_819efbc4-5cd9-4177-b826-e4a69b397b86.jpg[/img] 
^ this is similar to what our APC looks like, just replace the machine gun with a RR mounted like so:
[img]http://www.m201.com/02743/image006.jpg[/img]