Cathodic protection is old technology, just not common in the automotive industry, although it has been around for a while.
Even with the there is still going to be rust. Anything isolated by a ground will be that much more suceptable to rusting.
To be effective you'd need to place strategic sacrifial anodes around the vehicle. These are tabs that are more prone to rust then the common steel on your vehicle.
Zinc is one of the more common anodes used in places like the oil industry.