how about this:
The steel piping would require the robots to limbo under it to reach the ramp platform (3/4 ply wood). PVC guard rails as oppose to lexan and a massive amount of screw suggests a ramp.
?? Could the 3 casters be underneath the ramp (MOBLE RAMP

), and form only a fraction of the full size object, like a slice of pie?
Perhaps if the ramp is moble then the flanges would keep the piece of pie anchared. But then again, how can a robot push a massive structure with 5 inch casters that requires 3 632 grams (8 pounds) or screws?