I dislike seeing posts go unanswered.... so....
Enclosed "open reed" calls, used as howlers, leave much to be desired.
Knight & Hale made/makes one, and I had the displeasure of owning one, once.... threw it away, once I learned to use a "proper" howler.
This type of design, in my honest opinion, should remain in the realm of the waterfowler (*as a duck or goose call).
Krusty