Deductions & credits

 According to the IRS, you can deduct these "lodging" expense "if your duties require you to be away from the general area of your tax home for a period substantially longer than an ordinary day's work, and you need to get sleep or rest to meet the demands of your work while away."  

In your case, he is not just "away," he has moved there to live.  

Living expenses are not in general tax deductible. However, there are exceptions. According to the Internal Revenue Service, temporary housing is housing that you live in when working on a temporary assignment for your employer that takes you outside of an acceptable commuting distance from your home.  This does not sound temporary, but if it was you can deduct under unreimbursed job expenses.

The IRS further defines "temporary" as one year or less. Temporary housing may include a hotel or motel, an apartment or a rented house. Any reimbursements that you receive from your employer for travel and living expenses you incur while on a temporary assignment are not taxable. 

Your employer will not include these reimbursements in your gross income on your W-2, nor should you include this income on your tax return. If you incur all or a portion of these expenses without reimbursement from your employer, you may deduct these expenses from your taxable income as unreimbursed business expenses. The IRS does consider any reimbursements for temporary housing associated with a permanent move taxable. For example, if your employer transfers you to a new office and pays for your relocation, the IRS treats those expenses as nontaxable moving expenses. However, if your employer also pays for you to stay in temporary housing while you finalize the move out of your former home, then 100 percent of those payments are fully taxable.

Be careful. If you live in temporary housing while on an eight-month assignment, the reimbursement for that housing remains fully deductible for the duration of your stay. However, if your employer and you subsequently decide that you will stay in your “temporary” location for another six months, bringing your total stint to well over a year, the IRS then considers your temporary assignment to be permanent. The date the decision was made to keep you there for longer than a year is the date that your temporary housing reimbursement becomes taxable. This applies whether your employer physically reimbursed you or paid.

I do not believe  you could get it passed the IRS for moving expenses either. Here is what they say about temporary lodging for a move:

You can deduct one day as part of transportation expenses-  you can deduct the cost of transportation and lodging for yourself and members of your household while traveling from your former home to your new home. This includes expenses for the day you arrive.

The day of arrival is the day you secure lodging at the new place of residence, even if the lodging is on a temporary basis.  You can include any lodging expenses you had in the area of your former home within one day after you could no longer live in your former home because your furniture had been moved.

If your travel trailer  meets these conditions, it  can  be a  second home . You  can deduct  interest paid on a loan used to purchase your  second home . You  can only deduct  interest for two  homes —your main  home  and a  second home .