You’ve seen it on TV. Gator-Grip fits virtually anything that isn’t round: hex nuts and bolts from 1/4″ to 3/4″ (7-19 mm), eye-bolts up to 2″… wing nuts, square nuts, …
EPDM or any type of flat roof necessary to build up. Dont let someone just bolt through the flat roof. Build up pads to mount the blocking properly.