I searched "furnace filters, ventilation" and got a bunch of results, aart's in there.
I imagine cutting it to size and using either duct tape for a temporary winter thing, or moulding wood sticks with small nails to hold it in place. I saw someone just stapled it up.
I saw this initially a while ago from aart and again in the search, they got it in a roll:
https://www.backyardchickens.com/articles/ventilation-baffling.75434/
Some times a baffle/ baffles will work well, like jalousie windows in the south. aart's use of cardboard up between rafters as a channeling / deflection idea is good!