I started looking at my photos when taking the headliner out. I think only the edges were glued. Insulation panels glued to the roof, but the headliner was not glued to the mdf board (or whatever material they are) sail panels. Although there was glue behind the sail panel boards and I don't recall why. The headliner and boards all came out intact. (headliner got ruined though...mice chewed holes in it and a section of insulation for nest/bedding.) Here are a couple photos showing what I was dealing with. It took time to remove but wasn't terrible. Install I'm sure that's a completely different story.