Obviously, that is not many miles... plan on having it thoroughly inspected by a mechanic. You will probably need new tires so figure $1,500 for that {regaredless of how they look} if they are in fact the originals - check the DOT codes. Plan on changing/flushing every fluid, belt, and hose but that should not add up to much more than peace of mind.
Lack of use is particularly hard on the internal coach systems - AC, furnace, generator, water heater, slides {if any}, awnings, etc. All of these systems will need to be run and thoroughly inspected by a professional so you at least know what you are getting yourself in to.
Also, you need to find out why it has so few miles and where and how it was stored.
Once {hopefully} you know what you are getting you can adjust your offer accordingly. A unit with less than 400 miles a year would make me very nervous and cautious but it may be the proverbial diamond in the rough. Good luck and keep us posted.
:C
