The weather strips slide into a channel around the edge of the flap, and are glued in with silicone. If the weather strips get damaged, they can be replaced without having to replace the entire flap. It is a bit of a chore to scrape the old silicone off of the flap and reinstall the new piece, so if you want to make it easier on yourself or if your flaps are scratched up and worn looking, you might consider
replacing the entire flap, as the new ones come with the weather strips already installed.