I also used plastic (nylon ?) trim tools to fit both the glass and locking strip, one of which looked very similar to the one you've posted.
For some reason it took longer to get the glass in the gasket than the final locking strip but I have no doubt that if I'd had the tool that John's posted it would have made fitting the locking strip easier. I just didn't have one and being very Scrooge-like didn't want to buy a tool for a job I hope never to have to do again !
Brian