Rear window stainless in a shoebox

[Bruce Compton, Canada]

HELP. I've spent two days trying to fit the double groove stainless trim into the new Carpenter rubber and still can't get it in. Is there a secret trick I'm missing or a certain procedure to follow? I have the rubber mounted onto the glass but can't get the stainless to fit. I'm assuming that you start with the inside groove first but don't know for sure. It's a '49 Coupe but I'm using the double groove rubber as I already had a really nice double groove stainless piece.