I am not looking forward to that little chore myself. I have been completely stripping everything and then treating it with phosphoric acid to get any rust pits that may be left behind. For me getting the bulk of the rust off and treating the under dash area with phosphoric acid doesn't seem practical or necessary. Eastwood had a sale on their rust encapsulator and I bought a couple of spray cans to try just for this area. I have not wanted to use this product in areas I can get to but hopefully it will work well for under the dash.
Chuck
