There was a story in Friday's St. Pete Times, first section, which gave real
downtoearth instructions about this. I know SPT is online - you can try finding
it.

It says to have the plywood four inches larger than the window and to put small
holes in center of plywood to relieve the pressure. Recommends screws over
each corner and then across the top and bottom every so many inches.

We used tapcon screws. We store the plywood in the garage between uses and
it's lasted several years. We have put it up several times but it never got
wet. We pieced several smaller pieces together (found some stray plywood that
had been discarded) and it's thicker and heavier than what you buy (but free)
to cover odd size windows.