I have just finished fitting the rear windscreen.
It isn't a job to look forward to but I found a useful item that seemed to make the job a lot easier. Maybe everyone else knows about this, or has a better idea, but I'm posting this so it might help.
Attachment:
Tool for windscreen seal install.jpg
I normally use blunt screwdrivers or paint scrapers but they can, and did, nick the rubber seal.
The tool sold to insert the filler strip does a good job at this - the round section wire is less likely to nick the rubber seal. I also used rubber grease on the seal as the usual detergent solution dries out so quickly.