I got a used vinyl retrofit window from a friend (see picture) and am going to install it where there is not currently a window. I have the r.o. prepared and the sheathing on the wall. The siding will be stucco. The problem is the window is a retrofit window and doesn't have a nailing-fin. How do I properly flash the window? I want it to match my other vinyl windows, which are flush with the stucco and not recessed. This will be my first remodel and I am at a loss as to how to flash this window. Any help will be greatly appreciated. Thank you.