I've read a lot of reviews for solar powered window vent fans for cars and all the ones I came across had a ton of "this is cheap crap, don't buy it" feedback. I'm interested in buying one (overkill is the best kind of kill) but it's made me very uncertain.

I was also thinking of making my own, there are solar powered chicken coop ventilation systems that look reliable (since expensive chickens would die if they weren't I trust the quality a bit more) and I can 3D print the over-the-window ducting. In case the overkill isn't over enough.