The last three cars I had all died from rust in one form or another. I could keep them going mechanically but once significant rust damage sets in there's really nothing you can do about it. It reaches a point where they won't pass inspection.
I have my 3 new cars undercoated with NEOU. The actual undercoat is a wax/oil combination that dries hard. I bring them in every 2 years for a steam wash and a touch up application for $100; $1000 per car over 20 years. I think of it as relatively cheap body "maintenance". I figure that, while it might not stop ALL rust it will probably limit damage to something that is more manageable/treatable.
I'll let you know in 20 years how it works out.
