You can use minerallacs (minnies)one for the truss and one for the conduit for single runs you use rod to drop down or bolt directly back to back for a tighter arrangement.
If you want to span two trusses you can use the minnerallac on each truss drop to rods and support a section of strut to run conduit on.
If you want to stay tight to the truss bolt the minnies directly to the strut.
minnies are cheap!
For a heavier duty expensive rack you can use double strut using a strut strap to the truss and then you can install conduit on top or bottom of the strut.
There are many sweet strut clamps to choose from just, have to pay the price. I prefer B-line brand. but Uni-strut or kindorf are fine products