I'd just use styrofoam and seal with spray foam. Maybe consider wrapping the new PVC pipe with a bit of pipe insulation on the inside for a foot or two, for the reason that if cold air comes into the pipe and starts going inside, you are probably likely to see condensation forming on the pipe, where it goes through the screen and inside where the pipe is colder than the air.

I'd also consider some kind of one way valve or flap on the outside of the pipe to keep cold air from flowing into the basement. You'll have to be a little careful to check that the flap is never impeded and it's always working and free to open