Once you obtain the VIN, which will be the chassis #. The MH manufacturer # is important when trying to track down parts, wiring diagrams, etc but you won't gain a lot of information from it. You can get a AutoCheck or Carfax report by going to their website, submit credit card and VIN and you will get a report about registration, title, and mileage history, any insurance claims, etc. It doesn't give a mechanical or systems report, so you won't know if it has a rebuilt transmission or bad generator or things like that.
By the way, the VIN has encoded in it the year and other chassis information you can learn from the manufacturer or google 'reading VIN number' Don't be surprised if the chassis is a year older than the RV, the chassis are ordered ahead by the RV company and then used as orders are filled. It's not unusual for an '05 to be built on an '04 chassis.
Bob & Donna
'98 Gulf Stream Sun Voyager DP being pushed by a '00 Beetle TDI