I think someone is telling you a story to get you to buy one. As far as I am aware, you can only deduct on primary residence. Now, if the trailer IS your primary residence, then have at it.
Just verified this with my tax accountant.....
You can take a deduction on primary and a secondary residence. If you don't already have a vacation home or rental property that you're taking as a secondary deduction, an RV or travel trailer (with kitchen and bath facilities) qualifies. Most people don't know this and don't take advantage of it, just thought I would pass it along.
BTW-scratched a check for a 26' fifth wheel with slide this morning. Having the hitch installed tomorrow. Will post pic's when I can drag it home :D