lol, you could use just about anything to seal that off. How about a plastic container lid with a slit and a hole cut in the middle for the wire, if you want uber cheap 'cuz it's something you already have lying around?
You could use a fitting like some suggested, or use spray foam, or clay, or a piece of cardboard coated with epoxy or caulking, or a piece cut out of plastic or wood, etc... Wood, isn't waterproof, but it's going to keep water out every bit as well as the big open hole did.
Then again, a proper well finished looking plug is only $4 or less, so might as well show those lizards that you mean business.
Last edited by Dave9; 03/21/20 01:56 AM.