A real big old beach towel makes for the best mat to catch falling parts. Things can still ping and bounce away on cardboard sheets, but the towel will just stop it instantly where it falls and all you have to do is lift the corners to make the part go to the middle of the towel for you to gather up quickly. You're just asking to lose more of your parts if you keep working on that open slatted deck without anything to catch you parts if they fall.
Chombi
84 Peugeot PSV