1) You want some sort of cord that is about 5mm thick but no thicker
2) and then fit the rubber to the glass and fit the cord in the groove of the rubber all the way round.
3) Start the cord at the top of the rubber then across and down the side, continue across the bottom but stop in the middle and leave about 12 inches of the cord hanging out of the rubber and tape it to the inside of the glass.
4) Continue across the bottom after taping the cord and this will give you some cord to pull on once glass is in position
5) continue cord up the rubber on the opposite side and meet at top where you started.
6) Once you have the screen in place make sure that any cord hanging is on the inside of the car
7) start pulling the cord from the loop you left at the bottom working to a bottom corner and about 6 inches up one side.
8) Do the same for the other side and this will make the glass central in the car.
9) Once this is done make sure all the rubber at the bottom is lipped over and pull down on the glass to seat the rubber fully home.
10) The next step is to start pulling the cord up one side at a time and about 6 inches across the top
11) do the same for the opposite side and gently tap the glass with your palm to push the glass in if need be and finally pull the rest of the cord you have left and it should pull out completely and lipping the rubber over as you pull it.
12) Check all the rubber has lipped over the appature and hey presto. If you want to aid the rubber then spray some sort of glass cleaner around it that will evaporate but don't use fairy liquid as it will take ages to evaporate and can help future leaks and corrosion.

Phew got there in the end.