I typically use thin CA AND a 2" wide strip of 2 oz fiberglass on the joints (CA to the inside of the cowl ). I also CA a strip of fiberglass around the back side of the cowl to re-inforce the screw holes so the cowl will not crack in those areas.

After the cowl is assembled, I normally use spot putty to fill the seams on the outside of the cowl.

For ABS/plastic cowls use thin CA for assembley - epoxy will not provide a strong joint, and depending on the cowl material, may damage the cowl. For a fiberglass cowl you can use either CA or epoxy - I still suggest using thin CA though.

Hope this is of some help.