You can make these things out of rebar just make sure your slide lock is plenty oversize. You won't have any problems with it locking up on the reverse.
However, I too could never see the practicality in these things. If
you were trapping off the road, out of truck, they might be okay, but anything over eight feet is going to stick out of the truck. Otherwise, they are too heavy and awkward for my taste.
If there is somebody around here that actually does use them, maybe they could offer a positive comment.