Eric,
Yes it is deductable as a second home. However there are several rules which apply, such as must stay in 15 nights a year, must be totally self contained and have kitchen and bath with shower. There are several more rules, check with your tax accountant. This also applies to boats which are self contined.
Jim
I don't have personal experience with deducting interest paid on an RV as a second home; but do with a typical second home situation. The IRS publication lists the specifics on page 2 of the document linked below - - page 5 also has some further clarifications.
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