If you're talking about the division bar, make sure the old piece is removed. I remember there being a finger at the bottom and maybe a rivet up higher? The old felt channel needs to be removed as the new one will be a snug fit and trying to install one over the old piece is impossible.
If you're talking about the other u shaped felt. The bottom is held in at the lower detachable bar. I don't glue or screw anything. I use the inner window trim to hold in the felt u channel. I shape the felt in to the door, install the glass, roll it all the way up to hold the felt in place, then install the inner window trim.
