I have plywood, with the outside face painted flat black, screwed to the window frame. I left the dark blue curtains in front of the plywood, be sure to leave the folds in the curtains so it looks natural. Theres a rectangular hole cut in the wood over the open side of the window. I built a vent box to mount to the plywood which covers the hole. My exhaust fan and air cooled hood both vent into the box and out the window.
I use the box to allow the cooler exhaust fan air to mix with hot air from the bulb before going out the window. My attempt at reducing my heat signature. The box also dampens out some of the fan noise too...