Mine is bolted into the rear Plastic behind the Guage cluster using the MoTeC studs and extensions, I doubt there's enough vibration in a street car to effect it.
The Al sheet is only a facia and plays no part in the mount, If you're using solid engine mounts or if the car is a race car or offroader I'd look at using some bonded rubber instrument mounts (RX7 Radiator or Oil cooler mounts work well)
Having said that though watching the Paris/Dakar offroad race this year on TV I didn't see any dashes that looked to have flex mounts
