@Jim554
Jim please be careful. I can't tell you how many posts we have seen of guests who have used hosts property beyond the perimeter of the property and have come to grief.
I would not think that any insurer would accept your risk where you are allowing STR's to use you equipment on public property unless you run a licensed vehicle rental business.
And remember, a guests insurance policy covers them for their car, not yours!
The other thing to consider Jim, damage waivers do not automatically stand up in a court of law, in fact, most are open to challenge. Unless the equipment is certified, it can be argued that the equipment was not maintained in a fit state for public use!
I would not for a second consider doing something like this, even in Australia where we are a far less litigious society than you are in the United States.
Absolutely too big a risk, what happens if you let an Australian or British guest use the car where we drive on the other side of the road?
Do yourself a favour, don't mention the car Jim, if you do you are opening a can of worms, believe me!
Cheers.......Rob