On the face of it it seems to be:
Clean both faces REALLY well.
Put PU adhesive sealer on (Tiger seal or similar)
Lower screen into place with wedges to centre it
Put tape up onto roof to hold it for a few hours
Job done, remove tape, fit wipers.
Or have I missed something???

Should i just get a friendly fitter to come and do it, I have the glass?
PS. i'm not quite ready to do it yet, just thinking three steps ahead all the time.