No you just buy the rock n roll mounts / springs and buy some marine ply or what ever you want (Marine ply is best) and then just cut the bed to whatever width you want.
Most vans with cabnets have smaller beds, but i wanted maximum room and a spacious feel, so full width bed was for me. My last bay had everything and i wanted to go mimial but practical this time.
You can get the rock n rolll stuff from people like Just kampers, or peak em up cheap at a show 8)
If you look at the foam on the rear seat its benn fasioned so that there is a slight bump in it, to stop you slipping forward when on it. Plus it does give you a good ergonmic sitting postion. (great whe you have some mates in the van for those card evenings when camping :wink: