when i did mine with the tape, i put it on the metal surface. i put all the molding clips in first, and put the 2 little rubber spacers which come with the tape on top of the L-brackets. after putting the windshield in place, i went around with the caulk. this was all with the help of a friend who worked in a body shop. we pushed in on the windshield for a while before using the caulk.

IIRC, the rear window has no brackets to hold the glass up, so you really need the little rubber spacers if you do the rear window. we had them for the front, so we used them.