You're talking about putting a fixed windshield in, and the joint in the middle is referred to as a v-butt. Like leonard said above, you can have them cut the joint on an angle, and use as S-10 rubber to finish the edge of the glass. Paint the outer 1" or so of the glass black on the inside first so that it hides where you urethane it in. The best thing for the middle is to use poster-paper to keep the halves separate and give a gap when you install it, then remove the poster paper and use aquarium seal (found at any pet store) to seal up the joint. Works like a charm.
