Whenever you are dealing with taxes you have to realize that there is a little thing called "facts and circumstances" that plays into what can and can not be deducted. Do you have a legitimate business purpose for the expense? How much personal use do you utilize on that asset? Is it possible to deduct an RV in a business? Absolutely, if you have the right set of facts and circumstances.
If I'm a doctor who has an office practice, it's darn tough to justify writing off an RV. On the other side of the coin, if I'm in the business of supplying RVers and use my RV in that business then I would have a legitimate reason to write off the rig.
Facts and circumstances are the telling item with any deduction.