I gave up on Avis quite a while ago and now use Hertz in either of the following ways:
Quidco/Hertz.com/BD CDP/Prepay
Hertz.com/BD CDP/Pay Later
In both cases, if there's a #1 Gold desk at the pick up location then I call after the booking and add my #1 Number post-reservation.
If there isn't a #1 Gold desk then I leave showing the card until pick-up and, on many occasions, the agent has added in a 5% Gold discount there and then.
Why this perversion? Because 99 times out of a 100, if I log in to Hertz with my #1 Club Gold number, I am quoted a more expensive rate than if I don't use their barmy discount loyalty card.....
PS. Occasionally though, Marriott have offers for Elite members that have useful discount codes and Amex Concierge has just given me the best rate by far at YVR. YMMV.