I just enrolled. I am doing back to back to back monthly rentals and the base LDW/CDW doesn't cover this. It will only cover one 30 day rental even if you switch car rental companies. The Premium Amex insurance will cover back to back monthlies as long as you close out one contract and open a new one (even if you keep the same vehicle).

From Amex's policy:
"Note: In no event shall coverage be provided when the Cardmember rents a Rental Auto beyond 30 consecutive days from the same Rental Company, regardless of whether the original agreement is extended, or a new written agreement is entered into, or a new vehicle is rented.

Additionally, no coverage will be provided when the Primary Renter rents a Rental Auto for more than 30 consecutive days out of a 45 day period within the same geographic market/location (75 mile radius)."

I ended up choosing the $17.95 per rental option in CA over the $15.95. For $2 got a little more coverage (although likely not needed). The regret for $2 would be super high if it ever does come into play.