I spent some time smoothing the both inlets to the cowl, then laid up 5 layers of carbon fibre under the front edge of the top cowl. When that was done I pinned the two halves back together and wedged the edge into the right relative position. When this sets, the carbon should hold the rough shape I need and stiffen the front edge sufficiently to stop the airflow causing trouble. Later I'll put release tape on the leading edge and lay up the shelf for the top cowl to lay on.