Second home purchase and expenses. Can a 5th wheel recreational vehicle be considered a 2nd home? Can purchase expenses be deducted?

It can be considered a 2nd home IF it meets the IRS definition of a home:  it must contain sleeping, cooking and toilet facilities. If it qualifies, the interest on the loan can be deducted as 2nd home mortgage interest. Otherwise, you cannot deduct the loan interest. 

Mortgage interest data entry (if qualifies):

1. Federal Taxes
2. Deductions & Credits
3. Your Home, select Mortgage Interest a Refinancing

And yes, you can claim sales tax on the purchase:

1. Federal Taxes (Personal Self Employed version)
2. Deductions and Credits
3. Scroll down to Estimates and Other Taxes Paid, select sales tax