I just shot off of one of those flat bed golf carts. The grips rigged a mitchell plate off of speed rail that went across the bed and was held down with ratchet straps. You could do the same with a sheet of plywood or a plank with a high hat bolted to it that is ratchet strapped to the cart body or chassis. I don't recommend sitting in the cart wearing the rig as the g forces could easilly throw you off. It is just too simple to rig a hard mount.
Larry, your story regarding the cherry picker begs me to tell of what happened on a shoot I was on a week ago. Between takes on a night shoot as I docked the rig I heard a terrible noise. As I looked up I witnessed a 60' Condor with 2 18k lights and an electrician fall over, hit another unmanned 45' Condor and knock that over as well. Lights, 4X frames,grip rigging and tree limbs went sailing through the air and crashed to earth making a series of terrible sounds I never wish to hear again. The electrician survived with a broken leg, ankle, and orbital bone. Lucky to be alive and miraculously no one else was hurt. Most unbeleivable thing I have ever seen on a set (with the possible exception of Dolly Parton's breasts). Still no explanation as to what caused it. No wind and on level ground.