If available get the hinged front window. It allows the front window in the canopy to be folded down for cleaning the rear truck window and the front side of the canopy window. Without this option the only way to clean the window is to remove the canopy or at least slide it back. I think it was a $25-$50 option when I bought my ARE canopy.

 

http://www.fleetwest.net/DS170.html

To the OP: Someone else linked this site that I bookmarked (thanks), and, were I starting from scratch I believe I'd have a long look at the cab high DS-170. I like the idea that I can customize it to some extent, but most of all that I can "drive out from under" the enclosed shell as it is also freestanding. Use the truck for some other work. And then get back under it. Or, swap loads with another truck. Etc.

I believe there would be a penalty in aero resistance fuel mileage versus what I have now . . . sig will tell you I also have some margin. Wouldn't fit as close as current piece.

As to windows I don't miss them. In fact I need to replace my broken-by-a-criminal glass window with a factory fiberglass one if that is available.

I don't anticipate carrying humans or animals in back and I don't need to "see" in from sides . . with a plastic bedliner you just shove your tubs, etc around like a Rubiks cube.