glass block window
The best substrate to install glass block into is masonry, as in directly to your block, poured concrete or stone foundation. It's virtually zero maintenace, stronger, waterproof & you have more adjustability this way. Inside, you can fur wood right into it. Installing glass block over wood or the like will require caulk & alot more expensive materials, & they are all "temporary" compared to the life span of a good masonry install. I would suggest looking in the phone book for a local glass block company who can pre-fab the window for you. They have far more block availability to do custom sizes, & in my experience are cheaper than the big box stores. As a mason, I realize how tedious glass block work is & have them make all my window panels, as it saves me time & money.