This is how I make my torsion bar suspension by using 40x40x25 sqr tubing and 25x25x30 sqr tubing
and 4 pieces of latex rubber 18mm (this is from spear gun replacement of rubber band )
I have made some simple tools to help me press the inner sqr tubing over the four corner rubber insert(you must use liquid sop when pressing together)
Here is the complete suspension with 1,2,6,7 road wheel set hard and 3,4,5 set softer.
The torsion bar assembly is held by the center bolt in the supporting frame