I applied trim to the flooring and ceiling of both tower bays. But they come with window seats and those have to be installed.
Just like with the kitchen bay, it is difficult to get the window seats to fit when the walls are already in place but if you want a finished interior, you will have to deal with the difficulty and work around it. The best way to do it is to cut down the pointy sides of the window seats so they fit easier.
They don't tell you specifically where to put them on your tower bays so I just put them under the window, giving enough leeway for the bottom window trim to fit. I painted the window seats white.
Once they were in place, I made upholstery for them. I am not good with fabric nor do I like sewing, so this upholstery is pretty simple.
I just made a template of the window seat on poster board and batting. I used hot melt glue to glue them together and then wrapped them in fabric like a gift. Pretty simple, but of course, a little sloppy. That's fine because once in place on the seat, the application of trim and fabric flowers to the front hides any imperfection. I applied the trim to the kitchen bay window seat as well.
Simple thin batting or felt works best for these seats, rather than foam. It just makes covering with fabric easier but if you are nifty with sewing, you can make more detailed and elaborate upholstery for your seats.
I recommend you use some kind of cover for your seats because they will not fit perfectly into the bay opening and will have some gaps along the walls. Upholstery really covers everything very well. If you are fabric challenged, you can always apply wallpaper to their tops to create faux fabric.
