Even with thin tube a brew rig is still going to be pretty heavy. The simple answer is that getting it in and out of the truck is a two person job. Even if it's not heavy, it's big and awkward.
Indeed people do set up gizmos to pull caps on and off a truck all by themselves. If you want to do something like that, then yes you can easily put a 500 lb brew stand in the truck. Just how you get it out once you get to the other end .. not quite so clear.