The GIS map designates it as a single-family dwelling, but the property is clearly set up as two units, with separate HVAC, electrical systems, etc.My main question is: Would it be possible to obtain a permit to legally convert it into a two-unit property?

There are legal implications to being willfully deceptive to obtain a financial benefit for yourself. 

Have you obtained any detailed cost/benefit analysis quote?

(There are other ways to obtain/develop that evidence - such as using certified mail or my “practical advice” below.)In your case, because your friend found the letter inside the mailbox of the last known address, you now have specific evidence of having mailed the letter “…by first class mail, to the tenant's last known place of residence” - “Unless other arrangements (had been) made in writing by the tenant…”Again, in my (non-lawyer) opinion, you’ve complied with the letter of the law as to your concern - “Unless other arrangements (had been) made in writing by the tenant…”[Practical advice: Where I self-manage, in my “Notices” section of the lease, besides my physical address, phone numbers, etc for notices to me, I provide two email addresses for myself, and state in that part that email is my preferred method of communication.

AirDNA states: “Average yield is calculated by dividing the average annual revenue potential of short-term rentals in proximity to the national park by their average home prices obtained from Zillow.

Because it’s to difficult and time consuming to obtain, and when you do it’s just as likely to be false, or incomplete.  

If so, make sure agreement is in writing, signed by both parties, specifies new end date and ensures any existing security deposit will still be dealt with properly per landlord/tenant laws, and I'd also ask for a partial payment to be issued at signing to make obtaining his new place easier.  

Here is some free advice (worth what you pay for it):Upon application, obtain a handwritten statement from the borrower describing the intended use of the money.

The study identifies with forensic engineering detail the immediate Bonus Depreciation 5, 7 and 15-year personal property class lives qualifying portions of a building that are normally buried in 27.5 year residential or 39 year commercial categories.If you have had a cost segregation study performed on your property within the past 10 years, have you evaluated it recently for additional benefits that could be obtained?

Hello Everyone,I purchased my NACA home more than 5 years ago, and I obtained a HELOC on my home last year.The financial institution that approved and funded my HELOC was fully aware of the NACA Lien on my home and continued with the process either way.Also, I am not in violation of the occupancy requirements.What would NACA's actions be?