Here's what we do:
Buy an 18 inch square receiver tube (Northern, Hab. Frt. or TSC)
Buy ball mounts at the heights you need them
We use it with vise mount plates sometimes if we need to hold things for repair or cutting in the feild.
Also, we put an extension on one and added a light mesh carrier for tools. Works great, alot nicer than towing a cart around /forums/images/graemlins/grin.gif