i have a direct vent gas fireplace. The vent goes through the plywood wall but the hole in the playwood is an inch or two bigger than the pipe so there's a gap. We've been having mice get in our house in that area. How can I seal around the gap? The fireplace was installed when we bought the house and I think it was a DIY job so that's probably why there's the gap. Is it something I can fix myself? I have to do something keep the mice out. Thanks.