If its an IRS question, then I would assume you don't want to show it as rental income anyhow. You'd have to ask you CPA that.
I guess it depends on if you are getting a mortgage or not. And what kind of mortgage. If someone is paying you rent for 6+ months a year, it is an investment property not a vacation home. And investment properties are harder and more expensive to finance for you.
If I can be of any help, please let me know. Thanks,
I am a Realtor & an Attorney (30yrs), licensed for both only in Ohio, so I cannot & do not represent you. Therefore, what I write here is only my personal opinion. My partner & I had a similar sitiation within the last 6 months. For lending purposes, the loan was considered an investment loan (which meant a higher rate & a required down payment). The payments from the relative to the owner are classified as rental income, meaning investment income. This is is the case even though there is no lease of any kind, just an understanding that the relative is going tp pay the owner. Again, this is my personal opinion. I suggest that you talk to an accountant about the actual tax implications for your specific situation!