Thanks for the replies. The sketches are indeed limited. But they were meant to give a rough idea anyway.
My goal is to modify the RV's body and frame as little as possible. Ideally only the wall(s) between the cab and camper. Plus obviously the mounting points for the seat brackets.
If the truck's frame has the "hump", I'd definitely mount the seats higher. Not only to minimize fabrication, but also to have enough leg room for the passangers. The second seat row would mainly be for the kids anyway.
As long as our son won't grow to 6'5" or so in the next, say, 13 years, a higher mounted 2nd seat row shouldn't be a bigger issue...
It'd be interesting to know how campers are built in that front area, though. Some of them seem to have storage space/boxes there, others a door or sometimes nothing...