I'm glad you came to sensible solution for now. My other suggestion would be to involved your FIL in your finances, no details but info sharing on what might be helpful for them to continue the present arrangement as manageable as possible.
Just make him aware of some of the expenses that prevents you from giving him as much leeway on the thing he want to do with your MH, and other things he might have taken for granted and not aware of.Just be frank with him and tell him the things he is suggesting are fine but financial constraint is preventing you from doing it.