Looking for repair suggestions to our woody

So, first major damage to our 12-year-old woody. Coming home from camping today on a very rutted, rocky road, managed to pull a fender bolt all the way out of the wall of the tear. It is 3/4" solid birch plywood walls with multiple coats of epoxy followed by 4 coats of spar varnish. We will be doing the repair, as we figure since we built the thing, we can repair it. Looking for any suggestions and ideas on how to repair this awful, making me cry damage.
