Sounds like a good time to weld in a piece of steel to patch the hole. If it is going to be used as you say it wll, do you think it will matter? Even if you were to build it for the street/woods, the same would work. If you fix it and cover it up with a mat or carpet, who will know?
If you go to
www.webshots.com and do a search for "humps", you will find that there is an entirely different thought process. This has nothing to do with your post, but seeing your title, sure made me think of other items referred to as humps. Forgive me, I don't mean to sideline your question.