Even if you do, the car company can put a huge hold on your card.
I've read some bad reviews of Ecovia, and wonder if you might not be better served by Avis/Budget, Hertz or AutoEurope, who are much more major rental agencies.
Also, check your credit card's terms. Many have insurance that will cover the rental and there may be specific terms that would make opting for the full CDW invalid. I have an Amex for this purpose as it has great insurance and having a large hold on it isn't a problem as no one in Italy likes Amex to start with.