It's not deductible as a mortgage on the RV, because the loan is not secured by the RV. And it's not deductible as a mortgage on your main home, because it was not used to buy or improve your main home.
If the balance includes a balance brought over from a prior mortgage that was used to buy the home, then part of the mortgage is deductible. For example, if you bought the home with a $100,000 mortgage, and the balance was down to $90,000, and then you refinanced for $150,000, then the $90,000 that came from the original purchase is still deductible (60% of your interest in this example). Turbotax should help with that calculation.
