I've not had a lot of luck find anything firm but this is what I did.
When I was looking I called a couple of different providers and asked if they would insure my point rentals, most had no idea what I was talking about but after explaining it I usually got a no they couldn't.
so then I emailed TravelGuard and asked, I provided all the details in the email, and received a reply which said yes they could.
so I went on their website and purchased their "ProtectAssit" plan - All they ask for is the deposit amount and the total amount.
if I had to cancel I would have the email as "proof" that they should coverage my rental, but I wasn't 100% sure it was insured. The flights were and that was the larger cost so something would be better then nothing....
I don't guess this really helps...but there is their website:
http://www.travelguard.com/
in the end we had a great trip (wll excpet my kids got sick).
Todd