Better weatherproofing crawl space vents.

First winter in the new house and the downstairs floor stays cold as shite. Geothermal unit can’t keep up on the 1st floor and I came home to 63 degrees.

The vents are closed but they honestly look a little on the cheap plastic side.

Any downside to putting some foam boards into the vent space and doing a temp seal?(easy to remove for spring) or is there a better recommendation?