You want it, nobody else will buy this fall--chances are and with a 98/97? Old and the price is just OK. What is an 18 year old car worth? Then translate that to the RV chassis. You don't have a lot of choice in your area and if it meets your needs, stay interested, but don't rush into it.
Dirty? Is the carpet stained? How do you know the cabover is not rotten? What about the back panel? Did you look underneath? I mean on your back? How rusty is it? How well do the tank levers work? Any signs of leaks? Dark spots on the tanks etc. What are the tire codes? 
Could it be a 97 chassis and a 98 model RV? How many owners? State of the roof? Did you do the free check on the VIN number? I have friends who bought a Coachman of about that vintage and found they had LOTS of leaks in a downpour. Mentioned they might need a new roof. What will you do with it if it is in worse shape than you think? Have you had it checked out by a mechanic? Do the brakes have to be completely fixed? Bought a truck last year that needed new rotors this year and along with a check engine light problem with the fuel system cost me $1800. 
You said you have a lot of experience with older RV's so this may be worry about nothing. We knew nothing when we bought our RV but have had pretty good luck with it so hope you get lucky too!