As a CPA, perhaps I can answer your questions. First off you can deduct the interest on your RV as a second home providing you don't already have a second home that you are deducting the interest on. Second thing to look at is how much sales tax did you pay on your rig when you bought it. If that sales tax plus the tax from the sales tax tables is more than what you paid in state income tax then you can take the sales tax also.
One hint for you though. Do not show the interest on your RV on the mortgage interest line on Schedule A. Show it as other mortgage interest not reported on a 1098. This should keep you from getting a friendly letter from the IRS.
As far deducting the RV cost, you would have to show some business or rental purpose to take off any of the cost of the RV itself. If you do go that route, be aware that some of the use of the RV will be personal so you can't take the whole thing unless you don't use it personally at all.
I hope this helps.
2011 Berkshire 390bh