I have a 1999 fiat Ducato van and am considering ceiling replacement following major leak issue. Without ripping everything down I'm trying to first work out what is actually holding the ceiling in place! The seams on the outside of the van look like in this picture. This goes up the back and along the roof and from what I can make out the screws in this seam are screwed down into the tops of the wall panels. I cannot see what holds the ceiling panel onto the wall panels though - or how the ceiling is supported overall. Can anyone try to describe it to me please - so I can make a plan how to replace without first destroying it? Thanks