Frame it if you can!
Frames are like icing on the cake. They finish a sheetrock window opening. More importantly they adapt the shutter to the opening and they allow the shutter panel to be squared. They are the finishing element. Alternatively you can direct hinge or use a "Hang Strip" but you are always better off with a frame when you can.
Below are some popular frames. Many other frames are available. Not shown include Beaded L, Beaded Z, many adaptations of Knotched L Frames and Hang strips.
We recommend you avoid hang strips, direct hinge and inside mount L frames where possible.