Most HELOCS have an interest only period in the beginning.

They will mail you a letter to let you know if you pass or fall, and then you will have a time period to make any needed repairs (30 or 60 days, I can’t remember).

Would it have to be vacant at close or could the agreement extend an additional 59 days after close as long as there is a signed document by all parties?

There's a decent chance you will sell or refinance before that period, so the buydown was a waste.

This is especially true if you're only giving yourself a 6 month "trial period."

The lease extends to March 2023.

Period.

We had to extend our closing to over 90 days due to COVID impacts when we moved from California to Alabama. 

Obviously you will not go out an purchase a mobile home park today, but it is something that is possible in a short period of time.

Good to take photos so you can compare and if anyone does come back you can show that over X period of time you were at the home and nothing changed from week to week.You can be aggressive on this or less than aggressive, but good to learn your local laws and what is required to do to help you determined if it is indeed abandoned.