The IRS defines a home as "any house, condomininium, cooperative, mobile home, boat or similar property with basic living accommodations including sleeping, toilet, and cooking facilities." As long as you meet the above definition than you can deduct the interest on your trailer as mortgage interest on your second home. Keep in mind that you can only deduct mortgage interest on your primary and secondary residence (if you had a home, vacation home and a rv- only the vacation home or rv would qualify as a second home not both). Additionally you must itemize deductions to get any benefit from this.