Yes, that's true, but many of us use our rigs to sleep in while camping and leave the rear and back side windows open for good cross ventilation. I actually built velcro attached screens for the three rear windows and love the breeze without the bugs. Due to the vertical curvature of the windows, any rain at all comes right into the cab. Easily available deflectors for the side windows work and allow the window to be open slightly for fresh air, but it would be nice if there was something similar for the rear window that could be glued on or attached in some manner. Of course, for the reasons you mentioned, closing the rear window while the engine is running, especially when driving.