What chassis? If it's a Ford, I'd want to take a long test drive to be sure it doesn't suffer from any of the handling ills that have been reported occasionally.
On anything, the tires are 1/5 or more thru their 5 year life. Batteries are somewhat suspect, especially if exposed to low temps when not charged. If it has a gasoline Onan 2800, test it thoroughly to be sure it will carry rated load; they don't like to sit.
Negotiate price accordingly.
Jim, "My train of thought has left the station."