Make a $15 "Back-Bend" Brake
Actual Bend Height (90 Deg.)
= Height above bars + thickness
InSide Radius = 1 thickness
Start with (folded and taped) paper prototype for the flat pattern.
Trace the flat pattern on (double) cardboard, 1/8" cut (half though with box cutters) on top of all the DOWN fold lines.
Use bending brake for alum. and steel prototypes.