How do I emp proof my vehicle
Well, first, you have to realize that there really hasn't been much in the way of publicly available test data.
The data that IS available, (from 2008), is actually not bad news. Most vehicles only had minor electrical problems but were still drive-able.
The obvious route is to simply get an older vehicle. They didn't depend on the computers and microchips that more modern cars do, so they are more apt to keep running. This is far cheaper (even with a classic), than trying to shield a modern car.
Rather than making a car EMP-proof, you're better off just having spare components that would be affected, kept in an EMP-proof container. That way, AFTER an EMP attack, you could change out affected parts and be fine. (presumably).
Again, it's all guess-work, as we really don't have much publicly to go on.