I would recommend using ABS plastic for its strength. 

Layer height (mm): 0.25

Shell thickness (mm): 1.0

Fill density: 50% 

Lightly sand the base of the arms for the stand about 1 centimeter up, creating a rough surface. Put a layer of epoxy on the sanded area of the arms, and slide into the slots on the stand. Let the glue dry for 24 hrs before installing the triangle. 

Use fishing line to tie the corners of the triangle to the holes at the top of the arms.