I am going to presume you are not on title to the real estate on which the home sits. I would contact the mortgage company directly to see what can be done. At some point, however, he'll need to cooperate. Unless you have a written agreement with him that he was to allow you off the mortgage at a given time, not sure if you can force the issue. If you owned the real estate with him, a partition case could force the issue, but I don't belive that remedy is available to you for just a mortgage or an item of personal proerty like a motor home. Speak to a local attorney about that.
To questioners from West Virginia & New York: Although I am licensed to practice in your state, I practice on a day-to-day basis in Massachusetts. I answer questions in your state in areas of the law in which I practice, and in which I feel comfortable trying to offer you assistance based on my knowledge of specific statutes in your state and/or general principles applicable in all states. It is always best, however, to work with attorneys and court personnel in your own area to deal with specific problems and factual situations.