I believe barrel bolts on plywood which has been cut to size to insert in a recessed window can work very well also. The barrel bolts are fastened to the outside of the plywood and are pushed home into holes drilled into the masonry. A fairly simple system.
Hadn't heard about the hurricane clips until this thread, sounds really easy - are they rated for very strong storms?
"Hadn't heard about the hurricane clips until this thread, sounds really easy - are they rated for very strong storms?"
I don't know about any type of ratings......they've never let me down though.