Here is an old list of class B manufactures I posted in 2009. I would think most of them would still exist. Maybe it is time to update the list. I will start another thread for that in a day or two.
http://www.rvforum.net/SMF_forum/index.php?topic=25366.0
Personally I have a van I customized myself but I did have a Sportsmobile penthouse top added to it. If you really want to sleep 4 in a van I would really recommended considering adding one. They are not cheap. $5k-$6k range, but if we every customize another van we would add one again. Not only does it increase your sleeping space but makes it possible to WALK around in the van standing up when the bed is stored.
This movie shows our van w a SMB penthouse on it: http://www.youtube.com/watch?v=5Xqk_G6k95M
Of course they would be very happy to do the whole van for you. They have a plant in California, Texas, and Indiana.