I would ask him what he wants B4 I did anything else.
When U look at the threads on this site U will see where fixing a rotted floor is a major item of work,
Look 4 mold and test the appliances.
Then if the price is not out of the question, get under it and look at the frame to make sure it ain't rusted through, cracked, etc and that the suspension on the axles are OK. More than likely U will need new tires
Then if U think U have a fare price, go from there or point all the bad things out so U can renegotiate the price. He may just give it to U to get rid of it.