how hard is it to install rear window?

Had many windows installed by Pro's on My big Rigs. They always seemed to leak. They use a black RTV/Caulk but never seem to get it just right. If it was my car, I would get the best Black Window Goop I could find and then make sure it was a nice even layer. Then I would install it in the shade and press it down nice and uniformly. The I would move into the sun to settle it in nicely. A good Pro would probably get it right though. I don't know what the heck is wrong with the guys that were doing our trucks. Also, Be careful what you use. I heard that Silicone promotes rust aroung the window "Frame" Good Luck with it.