I attached some rubber sheets between the metal parts so that they don't slip (see attached photo).
Nitrile rubber sheets with sticky tape were used (RBTMA0.5-40 and other thickness, from Misumi).

Next
- Put some rubber sheets to the parts to support the tube
- Find one M10 nut (one missing to fix the Bar2 from top)
- Update AS optical layout to include AS tube and its supports