I don't know why I didn't think of this sooner but thought I'd share in case anyone else hasn't thought of this.
I purchased this aquarium filter material, cut it to fit in the intake vents, and it works really well to block the light from entering/escaping the intake ports (I got the 35ppi but 25ppi would probably be even better). One sheet is enough to make four 8" filters. https://www.amazon.com/gp/product/B093HHKSTZ/


Here's how it looks stuffed into a 6" vent hose

I purchased this aquarium filter material, cut it to fit in the intake vents, and it works really well to block the light from entering/escaping the intake ports (I got the 35ppi but 25ppi would probably be even better). One sheet is enough to make four 8" filters. https://www.amazon.com/gp/product/B093HHKSTZ/


Here's how it looks stuffed into a 6" vent hose
