Installing a window that is very unique to post frame construction. I am by no way saying this is the best solution...especially when looking for air tightness, but I suppose some good foam insulation would create a pretty good seal around the rough opening. Plyco makes some great windows and doors for this specific industry, and these are great options for those projects that are balancing aesthetics and function in my opinion. They install fairly fast, and the windows don't slow down the installation of your steel. Plyco - http://www.plyco.com/ ~-~~-~~~-~~-~ Please watch: "Building a Mancave 8: Porch roof and trim details" https://www.youtube.com/watch?v=M3np_jGJu5U ~-~~-~~~-~~-~