Oh this will not fill as much volume as you need. This is for plugging holes into a garage or through some other fire rated wall.

Rockwool insulation held up with string, and then poly sheeting stapled over that is probably the cheapest way to do it correctly with a high R value… Idk though I’m back to asking an inspector what they would accept, but I work construction so I speak to them. Your hardware store randos will point you in a better direction than me probably.