I have a early 60's house that I am replacing all the windows on soon. I have completely stripped the walls down to the studs and removed the old windows. There is a 2" gap between the brick and the sheathing. The new windoes will be mounted to the sheathing/studs but the big gap has me worried. What is the best way to make this water tight considering this large gap? The old windows relied on brick moulding and a lot of caulk but I can see they still leaked some. Anyone have a suggestion?