Both Thrifty Blue Chip and Dollar Express have not been accepting new members for a while now. They seem to be reevaluating or revamping (?) the programs. We have no idea when there will be further news on this front. If you're not currently a member and you want to skip the counter, you may want to look at renting with a different company.

Note that even if you were able to sign up, there is no way that we know of to add your member number to an existing booking, so it would likely require re-booking it from scratch which means that the price could be higher than what you are currently booked at.