I don't know anything about the venting of the kitchen yet so am listening in.
What I did and know works very well is the rear upper light on the driver's side. used the centre of the empty hole to figure out where to cut inside to enlarge it. It now has my 6" stove pipe running out and up into a 90* elboe outside. Took it up to just clear the rooftop height and capped and brace it up. No problems yet and goes down the road no problem up to 85mph so far. As far as safety, the hotter the pipes and joints get the tighter they get also when in use. Mine was so hot last Saturday it was too warm to stay in the bus and build. Was about -30 windchill all day.
Sorry to busy to post pics but if anyone might want a look I could email easier.