Any or all of the interior walls can be moved or removed, only exterior walls are structural. One exception might be in the case of excessive rot in outer walls. Lumber is generall less thick in walls and floor and roof. expect to replace subfloor as there are areas that tend to trap water and rot. How is the roof? Any low spots? This can be caused by truss pieces topling over. Plumbing lines are generall of smaller diameter than house counter parts. Mobile homes are full of short cuts in general that make them less expensive than a equivalent house. They are not all necessarily created equal, depending on the make, some are better built than others. The heat systems are generally simpler. Door frames tend to be shorter than the standard height. A bath tub is 4'6" rather than a full 5'. In other words you can't necessarily buy a replacement part or fixture or appliance in a home improvment center and expect it to fit. Some house replacements can be used with special adaptations.