There are several ways to do this. Based on the information you've provided, along with my understanding and interpretation of that information, here's what I recommend for the most tax benefit.
For your 2020 taxes, this property is nothing more than a 2nd home. Therefore you can only claim the mortgage interest and property taxes actually paid in 2020, as a SCH A itemized deduction on the 2020 tax return.
Since you will only be using the property for personal use for at most, 2 months out of the year each year, I recommend you place the property in service with an in service date of the first day a renter "could" move in, and leave it in service and classified as a rental for the entire year. You never take it out of service, and you never convert it back to personal use. Note that on the legal front, you'd have to be advertising this property for rent for the entire year, with the exception of the period of time you intend to use it for personal use.
We plan to rent it for 2 months in 2021
So your conversion date/in-service date would be the first day a renter "could" move in. It's important that you actually do get a renter in there too. On your 2021 tax return you would indicate you converted the property from personal use to residential rental real estate, with an in service date of that first day a renter could move in. You leave that for the remainder of the year. So if it's rented in Apr-May, so long as you are "attempting" to rent out the property for the remainder of the year, all expenses incurred from Apr thru Dec are rental expenses.
Now lets say you use the property for personal purposes in the month of June for the entire 30 day month. Assuming in in service date of Apr 1st, that's a total of 274 days the property was classified as a rental. Of that 274 days you have 30 days of personal use. So you report 244 days of "business" use as a rental, and 30 days of personal use.
The program will "do the math" for you to determine that 10.9% of the time the property was classified as a rental, it was used for pursonal purposes. So with only 89.1% of actually business use, the program will allocate 89.1% of your expenses to the SCH E. For the property taxes and mortgage interest, it will allocate 89.1% to the SCH E and the remaining 10.9% to the SCH A. For the property insurance, it will allocate 89.1% to the SCH E. (Property insurance is not a deductible expense for SCH A).
It works kinda like this:
You enter the total of all actual expenses in the SCH E section of the program that were incurred "AFTER" the in-service date. Then the program will ask:
In-Service Date: 1 Apr 2021
100% business use? NO
days of business use: 244
Days of personal use: 30
Program "does the math" and determines that of the expenses incurred, 89.1% of them can be allocated to SCH E.
