We have a such a blind, and are planning another later this summer. The wood floor of the wagon was good enough to use for the floor, and we just framed the sides with 2x4 and used scrap steel for the sides and top. I had an old door laying around that we put in, but it is something less than an air tight fit. I learned a lot about what to do differently for the next one, so hopefully the second one will be better.
We did use sliding plexiglass windows, and they work just fine. The original version slid vertically and we used a nail to hold them up in place. I have since changed them to a horizontal slide...much better! Here are a couple of shots of the windows. These are in a permanent blind we built, but the same design. We ripped grooves in the 1x4's for the plexiglass to slide, and a little weather stripping makes them very weather tight.
I don't have any pictures of the blind itself, but do have other window pics if you want to see them. They are 1 foot high and 2 feet wide...ideal for gun hunting, but if you wanted to bow hunt out of it, would need to have more of a vertical orientation.