I bought a 2006 Jeep Wrangler Unlimited about a month ago. It did have a little rust on the undercarriage, which I thought was normal for a truck. A friend of mine told me that he had his 94 Bronco given an undercoat by Ziebart. Is this a prudent step? I don't know If I will take it through mud, but I live in in DC area and they do salt the roads during the winter storm(s). I know there's a difference between rustproofing and undercoating, does it matter? Will the undercoating void my extended warranty?(I guess I could ask Dodge Chrysler). Thanks.

That rust proofing is generally not a great investment, especially in your locale. DC does salt like once every other year since most towns don't even own a plow. In Chicago we have had about 75 " of snow and an equal amount of salt and most people doen't do the Ziebart here either.