Fitting a K10 quarterlight

I have 1992 K10 5 door. The driver's side rear quarterlight shattered, not really sure why. I have a replacement glass and a good rubber. Anybody got any good tricks for fitting it? I know I should use a cord wrapped round the rubber and crossed over - but do I fit the window from the inside and extract the cord on the outside - or the other way round?
 
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