I have windows in a shooting house just like what you are describing. Have not had a bit of trouble with them except fogging. Especially when you cut the heat on. I have noticed that the overlap dont fog. My advise to you would be let a foot or so overlap in the middle. On a cold humid morning when you cut the heat on, that will be the only foot you can see out of without wiping constantly. That will still leave you plenty of sliding room as well. You can window a whole 4x8 shooting house for about $70.00. Thats what a sheet of plexiglass costs at lowes. Also, I made my windows 12inches high and almost all the way across all four sides. If I had it to do over, id go about 8inches. I have not had any trouble with water freezing in the tracks.