Additional info:
When he suggested that I put the MH at the beach I laughed because I foolishly thought he was kidding. The look on his face let us know he was not. So we told him that would not be happening.
AS for "allowing him" to live in our house for free. That is a long story but the short of it is that my wife wanted her parents to be close to our kids as they grew up. For my kids it worked out great. They loved it. For my wife it had its ups and downs as can be expected. For me it was OK when my mother in law was alive. When she died at 62 that changed. Since then my father acts with no regard for others in the house. An example of this would be:
The wife and I went away for Memorial day. When I came home and backed the MH into its spot I noticed that not only was my flag gone, so was my flag pole. When I asked my FIL about it he shrugged it off as no big deal. He said that he was sick of that flag pole so he cut it down and threw it away. Then he said it was his flag pole so he could do what ever he wanted. That was a day my love for my wife almost lost out to my desire to kill her father ;)
The entire thing is complicated. My wifes parent built the house in 1969. My wife bought it from them in 1987. In 1989 I moved in and have been paying the mortgage (with the DW) ever since. Because my FIL built the house he still thinks it is his so he does what ever he wants to. When a repair needs to be done he then remembers who owns the house and we pay to fix it. My wife feels locked into this situation and feels like she can never sell the house. To her it would be like putting her father out on the street. She does not want that and most days I don't either.
There is no happy ending for this story. Some endings are worse than others so we hope for the best. Owning a MH and being able to get away helps.