Greg,
we get some major winds here also, I have always done it this way and never had a problem, but I hear what you are saying.
I make my slit's horizontal and space them about 1/2" apart, good idea Mike has by backing them up with duct tape.
"Do you know of any marine elctricians? I need to wire a few things..."
Before you hire someone, ask the questions here, you may get the answers that will allow you to do it yourself.
Mike'second picture is what my shrink wrap guy does.
walter