there are 5 passenger doors on each side of the 747. The main deck cargo door is situated about 6 feet behind the number 4 passesenger door. In most cases the main deck freight will sit in that area between number 4 adn 5 passenger doors. there is of course a large next from floor to ceiling to prevent any pallets from sliding into the cabin in turbulant flight. From the passenger point of view there is just a wall at the back of the cabin with maybe a lav on each side of the plane back there. There really isn't a huge noticable difference for the passenger.