On a glass body you will have to attach some form of support to the inner rear fender well. Usually this is a block of wood suitable large enough to spread the load out and provide attachment. How far down on the fender well depends on a lot of factors, like brand of lift your using and how high you want it to lift the deck lid. With the lift fully retracted sit inside the trunk and close the lid. Position the opener in a position where it will not bind. Mark the position both on the fender well and the underside of the deck lid. Now open the deck lid, extend the opener and position it on your marks. If there are no obstructions or binding that is probably a good mounting position.