Ok , picture shows rear seat is not a stowage box like in the 251/9 . There goes that dumb idea , lol .
So , probably something like this , with the side bin having staggered rows . IRC , the 234/4 had a set up like this as well , plus odd shaped bins with staggered rows of ammo show up in many German vehicles with little internal space and a gun with large / long ammo
- I found this internal drawing on the SdKfz 251 site . The site moderator has no clue who drew it so take it as a " maybe "