I just measured mine up then went to Ace Hardware and got a clear piece of plexi, I want to say it's 3/8 maybe? possibly thinner. I like having it clear, only problem is its hard to tell top from bottom until you put it in upside down and it doesn't fit, but then just flip it over. I didn't do handle holes or anything....I also used a belt sander to radius the corners and sanded all the edges smooth, think about it being tossed around and catching a sharp corner on some vinyl. One other thing I did was leave it a little tall so the fold back windshield actually pushes on it a little making a tight fit on all sides.
I am in it for $30 and have a big enough leftover piece to make another one. It's cool because you can't even tell it's there when you look at the boat in the rear view from the truck and inside the boat you can hardly tell its there either unless its all water spotted. It stores nicely up against the wall of the walkway behind the observers seat too. It has to be one of the best additions to my boat I have done. Patrick nice idea on the etching, can't you get sanger stickers that look like etched glass on the website?? Only problem is if it's a clear one do you have the etching on the inside or bow side, it would be backwards when riding in the boat. That's why I have left all stickers off mine.
It's a great DIY project that makes a hell of a difference when its cool outside and decreases the cab noise down to nothing. Plus it will keep your cupholders from popping out when trailering