If you look at the rubber hold downs at the bottom of a typical window protector, it would seem logical that you could use these on the top or sides as well as on the bottom. You would have to frame the plexi though. IMHO Lexan would be better because it wouldn't scratch as easily as plexi.
The permanent ones are nice too. You get an "Awning effect" when you prop them open.
Have fun whatever you choose.
Today is a gift,
that's why they call it the present.