Apologies if someone has asked this before - I couldn't find it when searching the forum.

Can you purchase insurance for a hire car other than with the rental company?
My travel insurance covers our excess, however how do we insure the car to begin with? Can you do this cheaper through an alternate provider than the rental company?

For example, if I try to obtain a quote through Avis car hire, the quote is quite reasonable, however to add insurances such as CDW and liability it nearly doubles the price.

Can american car rentals rent out cars with no insurance? This is how I am reading the T&C's