CDW (and Loss Damage Waiver, which adds Theft Protection to CDW) is usually included in the rental rate that you see on a website. Note that these “waivers” just reduce your risk from a high amount (similar to the full value of the car) to somewhere between $/£/€1500 and $/£/€3000 depending on the car and the rental company. That lowered amount is called the "excess" or "deductible" and it's payable in the event of an accident.
SCDW (also called "Damage Liability Waiver" and many other names) is sold at the rental desk and it lowers the excess/deductible towards $0 (the amount payable can still be as high as $/£/€500 depending on the rental company, plus other charges for administration fees, towing, loss of use and more). Our "Full Protection" policy provides equivalent protection up to 50% cheaper†, with $0 to pay in the event of an accident and it also covers the additional accident-related fees charged by rental companies.
Check if your RentalCover Protection requires you to have the rental company's CDW.