Thanks for all the input, everyone.
I've been looking at some of the "step" type blocks referenced above, for instance, the Tri-levelers. It looks to me like none of the individual steps are big enough, front to back, for a tire to sit level on it, and a tire is always going to be bridging 2 different levels. Obviously this works, since people use them, but to me it's not clear that it's stable. It's also not clear how the wheels can be chocked with this setup.
So if all the rear tires are up on the leveler, where and how do you chock the wheels?