We use a scissor-lift style cart similar to
this. We attached the top from a plastic cart we used to use (something like
this) to it.
We attach wood (2X4's usually) every year to customize it to hold that years robot. Works well as an adjustable height work platform in the shop and the pit and for transport to the field. The plastic top makes a good place to temporarily put parts and tools while working on the robot. It's worked well for us for the past five years.