Like the others say,the front windshields will need some form of sealer,the rear(s) should be fine with just the rubber.
They're not subjected to the same wind forces as the front.
Personally I prefer to make the join at the top and seal it with a small drop of urethane sealant,any excess can be left to dry and removed with a sharp razor blade or you can clean off while still soft with some form of shop wipes or careful use of thinners.
This little
Tech Tip might help with the rears.
