Years ago I gave up on the understrength German trailer undercarriage.
Took it all off. I went to a junkyard and bought a old-model Olds
Toronado rear end. I had a welder make a subframe to mount it on and
bolted it to the bottom of the trailer shell. Hooked up the parking
brake to the surge mechanism. The long single leaf spring, big shocks
and 17" wheels were perfect for the job. Perfectly stable at 90 mph.