Hey bud.
Ok you can waste your time putting plastic on the window, which will make your temps swing everytime the sun hits it, or just spend a little and put a piece of timber over the whole window, fix it to the wall, use contractors acrylic to seal around the edges, then take a jig saw ( or do this before you mount the timber) and cut out your intake and exhaust holes. Then simply attach the ducting and run it where ever. With a bend or two you can avoid the light leaks.
Now the temps won't swing so much.