If you go to the IRS website and look at Publication 936
, it will explain what is deductable and what is not. Per the publication "For you to take a home mortgage interest deduction, your debt must be secured by a qualified home. This means your main home or your second home. A home includes a house, condominium, cooperative, mobile home, house trailer, boat, or similar property that has sleeping, cooking, and toilet facilities." So as long as the RV is used to secure the loan, and it is your only second home, then you can deduct the interest. If you have more than one second home, then you must decide which second home you want to use to deduct the interest. As Ray said, you can deduct your first home, and one second home.