What I did with my cowl was tack glue it together with thin CA glue. Then, to protect the ABS from heat, I glassed the entire interior with 0.75 oz cloth and epoxy. A very thin layer of glassing. It adds very little weight, but a whole lot of strength, and the glass reinforces your seam. The outside of the seam can then be lightly filled with Bondo and sanded smooth. Now it is ready for priming.

Patriot