I made up a bracket from a bit of 50x50 RHS & some inch & quarter pipe I had laying around so it bolts onto the ariel mount of the ARB bar.
I had made the rocket launcher itself 30 years ago so had to adapt it to the ARB bar with an easy on & off system.
I left a lip on the RHS so it fits against the back edge of the ariel bracket to stop the rocket launcher turning. A nut is welded to the bottom plate before the plate is welded to the RHS. I glued some rubber onto the bottom to help protect the bar paint. A simple wingnut with a little round bar.