Thanks Louis, I do my best work in the dark!
I read on a trailer sailer site where a glazier there recommended soaking the strip in soapy water. Maybe doing it dry is completely the wrong way, particularly after what you said. He also recommended using a piece of wood and rocking on the wedge to work it in. I'll be chasing more of the wedge tomorrow. I'm going to try Grippy rubber and Affordable boat windscreens plus two local glaziers here. There must be a supplier somewhere. I can't find the supplier that I bought the original wedge from.
The local boat builder said they do away with the frame completely now. HE also recommended using Sikaflex 295UV even the marine sealant 291 is not UV stabilised. I don't think it matters here because the Sikaflex is covered. In any case its paintable and sandable so if it does weather there is an alternative.
Do you ever start one of those jobs that you wish you had never got into??
Best of luck with the V Berth too. I had that narrow bit of ply there too about 100mm wide just under the deckhead, it seems its just a dress strip to cover the anchor locker.