Generally, you can deduct mortgage interest paid on your principal residence and one other home. In a new case, a couple took their motor home on the road during the winter. The home on wheels had all the amenities of a regular home, including a kitchen, sleeping quarters and bathroom facilities.
Because the couple spent at least 14 days using the motor home personally, they can deduct mortgage interest for this second home. (Dunford, TC Memo 2013-89)