I've been replacing all the old wood 40+ year old double hung windows in my house with vinyl pocket replacement windows. I have one window left, a large picture window with a double hung on each side of it. I took the inside trim off the picture window and I can take a putty knife and run it all the way around the picture window. Would caulk and the trim be the only things holding that window in place? I can order a replacement picture window, how would it install (the other replacement windows you can put screws through the side of). Thanks for any advice.