Seems I have a problem putting this on the back support thread.
I made a back support for a PL some years ago.
Besides being a backrest, it provided additional rigidy to the buggy which was seriously lacking before.
pic


Note that I have clamped the backrest to the side rails. Do not weld on the PL side rails as the material is characteristically Peter Lynn thin, will fatigue rapidly and crack.

Thanks for the info and picture. I thought originally that even BeamerBob's bent conduit was welded to the side rails, but it's also clamped. I understand your concerns about welding to the rails.