Honestly, the best way would be to drop a windscreen fitter a few quid.
It can be done diy, but just not worth the hassle if you have a leak, as when it comes out again it will almost certainly break.
The normal process is to use a wipe stuff with a little brush around the area where the goop seal is going, this is a rust inhibitor, and also de greases the area to help sealant to stick, the guns of sealant are seriously hard work to push the tubes, most places use a electric motor bit on these, then screen is lifted on by means of suckers, there are two wedges at either end bottom of the screen to set it's exact position, turning these as they are on a cam makes the screen higher or lower.
The side ones are same prep then pop into place, mine have always been held with 1" wide masking tape, never left a mark yet, that a bit of soap and water wouldn't move anyway.
tabetha