You want a bit of pre-tension. About 50 kg. This is to avoid an open flipper when ended on a side.
This can be done with 2 bundles of 4 sturdy bungees.

You also want the bungees as long as possible to avoid snapped bungees.

The seatbelt harness will have to take the full force of the arm, and this again to avoid snapped bungees. 14 kg of moving arm with high speed is a lot of force.