Okay...today I tried a new technique and it WORKED beautifully! Well, it doesn't look beautiful but it is on the underside of the trailer so I am not too concerned with looks. On the bottom of our rear cap there is a very rough cut hole that is about 3" wide in one area and then it tapered down to 1" wide. I could fit my whole hand into it so it was definitely a place a mouse could get into. I believe one of you told me a squirrel was getting into that hole. I put aluminum foil into it but the foil kept moving while we were driving so I needed a different technique. So here is what I did:
1. I measured the hole and how far into the hole I could get screen. Turns out 4"x8" was the magic number!!! So I cut a piece of scree that big, inserted it and drew the weird shape of the hole on the screen.
2. Then I removed the screen cut the piece out making sure to cut a larger piece than the actual shape of the hole. I just didn't want a bunch of extra screen in there in case it rubbed on any wires.
3. Then I inserted a piece of wire into the center of the screen and twist tied it. Once I inserted the screen I used this wire connection to hold it in place while I foamed around the outside of the hole to lock it into place. I foamed through the holes in the screen and around the entire outside edge.
4. Then I waited a couple of hours for the foam to expand and cure and then I removed the wire and voila! A mouse proof hole!
Now many of you are probably asking why I didn't just foam it completely shut. The dealership told me that sometimes when we drive through rain the water can get into the underbelly. If it doesn't have a place to drain or air out it can cause other issues. So I figured I would use some wire screen to let the water out, air in, and definitely keep the mice out!!! The only difficulty is foaming upside down, make sure it doesn't drip into your hair (don't ask) and that you put enough in there. It is not a pretty job of foaming but since I was unable to turn the trailer upside down I am pretty happy with the results!