I usually tack the 2 pieces together with thin CA (go easy with the CA, all you need is a drop).

Then put a 1 - 1 1/2" strip of fiberglass cloth (I use what ever I have scraps of - usually anywhere between 2 oz - 6 oz cloth. Koverall will work in a pinch also ) over the seam on the inside of the cowl and using a scrap piece of music wire (typically 1/8" - 3/16" ) adjust the glass and wet the glass down with thin CA. Use the wire to push the cloth against the cowl as needed.

I then go over the seam on the outside with spot putty (comes in a tube in the auto section of Wal-Mart, etc ). let dry, sand, prime and paint.