Just remember to make a shape like you added the profile in your intake on the sides and top of your exit slot in the cowls interior so it has the venturi effect scavenging the exit airflow for you.
I am curious when you added the cabosil what type of proportion was it, how is it to work with? I found microballoons are a great to thicken filler but it is still subject to sag even using balsa dust and talc. I had heard of cabosil but have no idea of how to use it properly (I like to be able to do some sculpting like you did on that cowl) and am looking for any advice you care to offer.