Typically no, but not a bad idea, especially in a soft sprung Sienna. I usually wind up on a slight slope, I carry leveling blocks, and always bias my level so our heads are slightly higher, which for me, avoids and early morning headache from the blood pooling in my brain.
I had one for a few years, best riding van I've ever had, best front heated leather seats my butt has been in.
For what it's worth, I added Firestone airbags to mine, the kind that tuck inside the Toyota rear coil springs. It sure helped when fully loaded with camping gear, sometimes towing