The things I knowingly ran into on my new to me 2002 were tires, shocks and all batteries had to be replaced. That is a chunk of change. I think that was about $3k plus extra. Depending on chassis (Ford or Chevy) other things should be discussed with your father-in-law.
Just what has been done on recalls or improvements. Example, I was told the fridge was updated for fire prevention. When I contacted the MFG, after purchase. It needed another update! It was free but had I not pursued the issue I would not have known. I did know thanks to rv.net it could be a possible fire hazard.
The one thing I spent good money on was steering stabilizers. Just to get the MH down the road the way I wanted to drive it. That is just a fwiw.
Look at PPL for what you are signing up to pay and what it is worth at this time. The memories using it are priceless.