To take the glass out, you have to remove the metal frame, which is held in to the door by several hard to get to and drill out pop rivets (6ish), and even harder to replace.
The frame is also held in by quite a lot of black mastic, which is messy.
Try dropping the glass as low as you can get it without taking the frame out, and sliding the rubber down the sides as far as possibleand then trimming the tops when you have got as much down the sides as possible.
They are about 12" long from memory.
Alex in Norfolk.