Venting a gambrel

hello, I have a gambrel style roof with a large dormer on each side. all ridges have ridgevent, but there is currently no intake venting. I want to add some but here is my concern. The house has a third floor, a little smaller than the other two due to being inside the gambrel. so the 3rd floor walls except for the dormers, run from the roof transition down to the floor leaving 4 dead triangular spaces behind them. this allows for the steep gambrel sections. these walls are not insulated at all. If I put vents in my eaves then I am opening these spaces up to the outside temps and there is no way to access them and insulate. I am concerned by this as I am in north east Penna. any advice appreciated.