No need for a PMS with only one.AirBNB and VRBO can handle things for you.In the end you won't save much time with only one STR.Plus, personal correspondence really works well to boost those 5 star ratings. 

As I’m nearing retirement, I just invested a similar amount in first trust deeds secured by real estate at 9.75%.

Since they are responsible for maintaining the relationship with you after the transaction closes, this approach adds an extra layer of confidence and security to your investment. 

At the very least you'll always know where you stand in any given situation, something few investors are secure about.  

I completely agree with @Ashish Acharya's points about the cost-effectiveness of a HELOC and the potential credit implications if it’s secured by your primary residence.

HUD 4000.1 (I believe) is the latest HUD handbook and it goes over all requirements for originating the loan, including but not limited to occupancy requirements and exemptions.FHA occupancy : "At least one Borrower must occupy the Property within 60 Days of signing the security instrument and intend to continue occupancy for at least one year."

Do you have any suggestions on how we can secure long-term financing under these circumstances?

It takes a lot of energy to thoroughly vet a deal and a borrower to make sure financing is secure.

Further, decline would result in loss of borrowers funds, resulting in having to pay back funds which are no longer available to earn income. in the case of using your home as collateral for the loan in question, the result is much higher monthly mortgage payments with no corresponding income offset, and much lower equity in the home.  

Quote from @Jordan Kaylor: I'm new to real estate investing and have secured a HELOC on my existing home.