Best place for ground under dash?

I am an electrician by trade and for all of our high vibration connections and any bolted switchgear connection we use a product from Thomas and Betts called Kopr-Shield. It's very similar to Never Sieze but with powdered copper suspended in a grease. It does several things but the main thing it does is it helps reduce the resistance in any electrical connection. Where this is helpful is if your bolted connection starts to work loose over time, the Kopr Shield "bridges" the gap and maintains the connection. Ideally the bolt will not loosen but in the real world, given time, vibration, and heating/cooling cycles they will loosen. One word of warning if you are going to use it, I find it best to open the bottle and wipe a little bit on everything in site first thing, because it's going to get there anyway and at least that way you know how it got there :D.