I have not seen anything that thin, that's why I suggested a relatively simple change that would widen the opening and allow readily available weather stripping. Moving the outer angle to the outer surface of the run channel would add 1/8" to the width. It might also allow the window to be removed easily. My power window operators use bolted clamps with rubber padding to grasp the bottom of the window, so only the glass comes out and nothing else.
Great idea! Yes, moving the outer top rail, outside of the U-channel should both allow the window to be installed with the frame in place and more space for a seal that would keep water out. I have ordered this flocked rubber window scraper seal and will try it!